final environmental assessment interchange …outside.transform66.org/documents...tier 2 final...

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FAIR

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MANASSAS PARK

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Town ofHerndon

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ManassasNational

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Washington DullesInternational Airport

West FallsChurch

Dunn Loring

Vienna

Prepared byPrepared for

I - 6 6 C O R R I D O R I M P R O V E M E N T S P R O J E C T

Tier 2 Final Environmental AssessmentInterchange Justification Report

FINAL

TRANSFORM 66OUTSIDE the Beltway

66Multimodal Solutions - 495 to Haymarket

AUGUST 2016

66

66

I-66 Corridor Improvements

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I-66 CORRIDOR IMPROVEMENTS PROJECT TRANSFORM 66 OUTSIDE THE BELTWAY

Commonwealth of Virginia

Virginia State Project Number 0066-96A-297

UPC # 105500

Interchange Justification Report

Interstate Project This document has been prepared and submitted pursuant to 23 U.S.C. 111 to obtain FHWA approval to add new access ramps/modify existing interchange ramps on a fully-controlled interstate highway.

Submitted August 2016 to:

Submitted by:

The request for reconfiguration of the interstate access points is approved for a Finding of Engineering and Operational Acceptability. This approval is conditional upon compliance with applicable federal requirements, specifically with the National Environmental Policy Act (NEPA). Completion of the NEPA process is considered acceptance of the general project location and concepts denoted in the environmental documentation. Wayne Fedora, PE Division Administrator Federal Highway Administration, Virginia Division

Mohammad Mirshahi, PE Deputy Chief Engineer Virginia Department of Transportation

Date of Approval Date of Approval

I-66 CORRIDOR IMPROVEMENTS PROJECT TRANSFORM 66 OUTSIDE THE BELTWAY

Commonwealth of Virginia

Interchange Justification Report

This document has been prepared to satisfy the requirements set forth by Federal and State Policy for changes in interstate access. It is consistent with the Virginia Department of Transportation’s Location and Design Division Instructional and Informational Memorandum LD-200.7, and in accordance with the most recent update to FHWA’s policy on Access to the Interstate System dated August 27, 2009.

Submitted August 2016 to:

Submitted by:

Prepared under the direction and review of: ________________________________________ ___________________________ Susan Shaw, PE, DBIA, CCM Date Megaprojects Director, I-66 Project Manager Virginia Department of Transportation ________________________________________ ___________________________ Randall A. Dittberner, PE, P.T.O.E Date Northern Virginia Regional Traffic Engineer Virginia Department of Transportation ________________________________________ ___________________________ Stephen L. Bates, PE Date NOVA District Location and Design Engineer Virginia Department of Transportation

I-66 Corridor Improvements Project – Interchange Justification Report August 2016

Transform 66 Outside the Beltway

Table of Contents

Executive Summary ..................................................................................................................................... i

ES.1 Project Background ........................................................................................................................ i

ES.1.1 Project Termini ........................................................................................................................... i

ES.1.2 Summary of Project Purpose and Need ................................................................................... ii

ES.2 Summary of Proposed Action ....................................................................................................... iii

ES.3 Summary of Findings ................................................................................................................... iv

ES.3.1 Operational Analysis Findings .................................................................................................. iv

ES.3.2 Crash Analysis Findings ............................................................................................................ v

ES.4 Conclusions .................................................................................................................................. vi

CHAPTER 1. Background ........................................................................................................................... 1

1.1 Proposed Tier 2 Action .................................................................................................................. 1

1.2 Project Development History ......................................................................................................... 2

1.3 Relationship to Other Highway Improvement Plans/Programs ..................................................... 3

1.4 Support and Commitment from VDOT, Regional, and Local Jurisdictions ................................... 4

CHAPTER 2. Purpose and Need ............................................................................................................. 2-1

2.1 Tier 2 Corridor Needs – Existing Conditions .............................................................................. 2-1

2.2 Tier 2 Corridor Needs – Future Conditions ................................................................................ 2-1

2.3 Purpose and Need Summary ..................................................................................................... 2-2

CHAPTER 3. FHWA Interstate Access Policy Compliance .................................................................. 3-1

3.1 Responses to FHWA 8-Point Policy on Interstate Highway Access Modifications .................... 3-1

3.1.1 Policy Point 1: Need for the Access Point Revision ............................................................... 3-1

3.1.2 Policy Point 2: Reasonable Alternatives ................................................................................ 3-3

3.1.3 Policy Point 3: Operational and Collision Analyses ............................................................... 3-5

3.1.4 Policy Point 4: Access Connections and Design ................................................................... 3-7

3.1.5 Policy Point 5: Land Use and Transportation Plans............................................................... 3-9

3.1.6 Policy Point 6: Future Interchanges ....................................................................................... 3-9

3.1.7 Policy Point 7: Coordination ................................................................................................. 3-10

3.1.8 Policy Point 8: Environmental Processes ............................................................................ 3-11

CHAPTER 4. Study Area .......................................................................................................................... 4-1

4.1 Overview .................................................................................................................................... 4-1

4.2 Project Location Map ................................................................................................................. 4-1

4.3 Logical Termini ........................................................................................................................... 4-1



4.4 Study Area Boundaries and Facilities Included ......................................................................... 4-3

Chapter 5. Existing Conditions ............................................................................................................. 5-1

5.1 Demographics ............................................................................................................................ 5-1

5.2 Land Use .................................................................................................................................... 5-1

5.3 Existing Road Geometry and Access Locations ........................................................................ 5-2

5.3.1 I-66 Corridor .......................................................................................................................... 5-2

5.3.2 Interchanges and Intersecting Roadways .............................................................................. 5-3

5.4 Alternative Travel Modes ........................................................................................................... 5-6

5.4.1 Regional Bus Service ............................................................................................................. 5-6

5.4.2 Metrorail and Regional Commuter Rail .................................................................................. 5-7

5.5 Environmental Conditions and Constraints ................................................................................ 5-7

5.6 Existing Data, Operational Performance, and Safety Conditions .............................................. 5-7

CHAPTER 6. Alternatives Considered ................................................................................................... 6-1

6.1 Alternatives Development and NEPA Screening Process ......................................................... 6-1

6.2 No-Build Alternative ................................................................................................................... 6-2

6.3 TSM Options .............................................................................................................................. 6-3

6.4 I-66 Tier 2 Build Alternatives (Express Lanes) ........................................................................... 6-4

6.4.1 Mainline Configuration Selection ............................................................................................ 6-4

6.4.2 Direct Express Lane Access Points and Crossovers ............................................................. 6-6

CHAPTER 7. Roadway Geometry ........................................................................................................... 7-1

7.1 Background ................................................................................................................................ 7-1

7.2 Preliminary Engineering Development ....................................................................................... 7-1

7.3 Design Exceptions and Design Waivers .................................................................................... 7-2

CHAPTER 8. Traffic Volumes .................................................................................................................. 8-1

8.1 Traffic Forecasting Methodology ................................................................................................ 8-1

8.1.1 Travel Demand Modeling Methodology and Key Assumptions ............................................. 8-1

8.1.2 Methodology/Key Assumptions for Post-Processing of Modeling Results ............................ 8-3

8.2 Traffic Analysis Scenarios .......................................................................................................... 8-5

CHAPTER 9. Traffic Analysis .................................................................................................................. 9-1

9.1 Microsimulation Methodology ..................................................................................................... 9-2

9.2 Traffic Operational Analysis Findings ........................................................................................ 9-6

9.2.1 Existing Conditions ................................................................................................................. 9-6

9.2.2 2025 Conditions (No-Build vs. Phase 1) .............................................................................. 9-21

9.2.3 2040 Conditions (No-Build vs. Preferred Alternative) .......................................................... 9-61

9.2.4 Intersection Traffic Signal Operations Mitigation Considerations ...................................... 9-105



9.2.5 Other Potential Mitigation Measures .................................................................................. 9-116

9.2.6 Microsimulation Summary and Recommendations ............................................................ 9-120

CHAPTER 10. Safety and Crash Analysis ........................................................................................... 10-1

10.1 Introduction and Background ................................................................................................... 10-1

10.2 Safety Analysis Methods and Tools ......................................................................................... 10-1

10.2.1 Qualitative Safety Analysis Methods and Tools ................................................................... 10-1

10.2.2 Quantitative Safety Analysis Methods and Tools ................................................................. 10-2

10.3 Safety Analysis Areas and Zones ............................................................................................ 10-4

10.4 Safety Data Collection .............................................................................................................. 10-4

10.4.1 Crash Data ........................................................................................................................... 10-5

10.4.2 Roadway Inventory Data ...................................................................................................... 10-5

10.5 Crash History and Safety Analysis ........................................................................................... 10-6

10.5.1 Qualitative Corridor Safety Analysis..................................................................................... 10-6

10.5.2 Quantitative Corridor Safety Analysis ................................................................................ 10-11

10.6 Future Conditions Safety Evaluation ...................................................................................... 10-18

10.6.1 Evaluation Approach and Process ..................................................................................... 10-18

10.6.2 2040 Safety Analyses ........................................................................................................ 10-18

10.7 Future Safety Considerations – No-Build and Build ............................................................... 10-24

10.7.1 Signing and Pavement Markings ....................................................................................... 10-24

10.7.2 Design for Merging and Diverging Areas ........................................................................... 10-25

10.7.3 Interchange Geometry and Configuration .......................................................................... 10-25

10.7.4 Recurring Congestion ........................................................................................................ 10-25

10.7.5 Mainline Shoulders ............................................................................................................. 10-26

10.7.6 Guardrail and Barriers ........................................................................................................ 10-26

10.8 Safety Analysis Conclusions .................................................................................................. 10-26

CHAPTER 11. Land Use Compatibility ................................................................................................ 11-1

11.1 Current Land Use ..................................................................................................................... 11-1

11.1.1 Fairfax County/City of Fairfax/Town of Vienna .................................................................... 11-1

11.1.2 Prince William County/City of Manassas/Manassas Park/Town of Haymarket ................... 11-1

11.1.3 City of Falls Church .............................................................................................................. 11-2

11.1.4 I-66 Study Area .................................................................................................................... 11-2

11.2 Land Use Plans and Future Land Use ..................................................................................... 11-3






11.3 Activity Centers ........................................................................................................................ 11-6




11.4 Utilities ...................................................................................................................................... 11-7

11.5 Right-of-Way ............................................................................................................................ 11-7

11.6 Land Use Impacts .................................................................................................................... 11-8

11.6.1 Direct Land Use Conversions .............................................................................................. 11-8

11.6.2 Consistency with Plans and Policies .................................................................................... 11-8

11.6.3 Potential for Induced Development ...................................................................................... 11-9

CHAPTER 12. Environmental Conditions and Compliance ............................................................... 12-1

12.1 Background .............................................................................................................................. 12-1

12.2 Environmental Summary .......................................................................................................... 12-1

12.3 Findings .................................................................................................................................... 12-6

12.3.1 Indirect Effects ...................................................................................................................... 12-6

12.3.2 Cumulative Effects ............................................................................................................... 12-7

CHAPTER 13. Additional Supporting Information .............................................................................. 13-1

13.1 Procurement Method and Funding Source .............................................................................. 13-1

13.2 Projected Construction Schedule ............................................................................................. 13-1

13.3 Ramp Improvements Phasing .................................................................................................. 13-1

13.4 Conceptual Sequence of Construction as Design-Build Project .............................................. 13-1

13.5 Preliminary Signing Plan .......................................................................................................... 13-1

13.6 Information on Comprehensive Agreement Performance Measures, Technical Requirements, and Concept of Operations (ConOPS) ................................................................................................. 13-1

Appendices

Appendix A – Letters of Support

Appendix B – Conceptual Plans

Appendix C – Traffic Models (DVD)

Appendix D – Traffic Analysis Methods, Assumptions and Calibration Memorandums

Appendix E – Preliminary Signing Plans

Appendix F – MWCOG Congestion Survey Results and Aerials

Appendix G – Tier 2 Final Environmental Assessment, Chapter 1

Appendix H – Transportation Technical Report (under separate cover)



Figures

Figure 6.1: I-66 Mainline Typical Section ............................................................................................... 6-5

Figure 9.1: I-66 Corridor – Existing Conditions AM Peak Period Densities (veh/ml/ln) ......................... 9-8

Figure 9.2: Existing AM Time Travel for I-66 Eastbound ..................................................................... 9-12

Figure 9.3: Existing AM Representative Hour Intersection LOS Summary .......................................... 9-13

Figure 9.4: I-66 Corridor – Existing Conditions PM Peak Period Densities (veh/ml/ln) ....................... 9-15

Figure 9.5: Existing PM Time Travel for I-66 Westbound .................................................................... 9-19

Figure 9.6: Existing PM Representative Hour Intersection LOS Summary .......................................... 9-21

Figure 9.7: 2025 Phase 1 Alternative, No-Build, and Existing AM Travel Time comparison for I-66 Eastbound ............................................................................................................................................ 9-24

Figure 9.8: 2025 Phase 1 Alternative, No-Build, and Existing AM Travel Time Comparison for I-66 Westbound ........................................................................................................................................... 9-26

Figure 9.9: 2025 Phase 1, No-Build and Existing AM Peak Period Speed Comparison for I-66 Eastbound General Purpose Lanes ..................................................................................................... 9-29

Figure 9.10: 2025 Phase 1, No-Build and Existing AM Peak Period Speed Comparison for I-66 Westbound General Purpose Lanes .................................................................................................... 9-30

Figure 9.11: Summary of 2025 AM Representative Hour Segment Densities ..................................... 9-34

Figure 9.12: 2025 AM Representative Hour Summary of Vehicle Densities ....................................... 9-35

Figure 9.13: 2025 No-Build AM Representative Hour Intersection LOS Summary ............................. 9-41

Figure 9.14: 2025 Phase 1 Alternative AM Representative Hour Intersection LOS Summary ............ 9-41

Figure 9.15: 2025 Phase 1 Alternative, No-Build and Existing PM Travel Time Comparison for I-66 Westbound ........................................................................................................................................... 9-44

Figure 9.16: 2025 Phase 1 Alternative, No-Build and Existing PM Travel Time Summary for I-66 Eastbound ............................................................................................................................................ 9-46

Figure 9.17: 2025 Phase 1, No-Build and Existing PM Peak Period Speed Comparison for I-66 Westbound General Purpose Lanes .................................................................................................... 9-48

Figure 9.18: 2025 Phase 1, No-Build and Existing PM Peak Period Speed Comparison for I-66 Eastbound General Purpose Lanes ..................................................................................................... 9-49

Figure 9.19: Summary of 2025 PM Representative Hour Segment Densities ..................................... 9-53

Figure 9.20: 2025 PM Representative Hour Summary of Vehicle Densities ....................................... 9-54

Figure 9.21: 2025 No-Build PM Representative Hour Intersection LOS Summary ............................. 9-60

Figure 9.22: 2025 Phase 1 PM Representative Hour Intersection LOS Summary .............................. 9-60

Figure 9.23: 2040 Preferred Alternative, 2040 No-Build, and Existing AM Travel Time Comparison – I-66 Eastbound ....................................................................................................................................... 9-63

Figure 9.24: 2040 Preferred Alternative, 2040 No-Build, and Existing AM Travel Time Comparison – I-66 Westbound ...................................................................................................................................... 9-65

Figure 9.25: 2040 Preferred Alternative AM Peak Period Speed Comparison – I-66 Eastbound General Purpose Lanes ..................................................................................................................................... 9-67



Figure 9.26: 2040 Preferred Alternative AM Peak Period Speed Comparison – I-66 Westbound General Purpose Lanes ........................................................................................................................ 9-68

Figure 9.27: Summary of 2040 AM Representative Hour Segment Densities ..................................... 9-74

Figure 9.28: 2040 AM Representative Hour Summary of Vehicle Densities ....................................... 9-75

Figure 9.29: 2040 No-Build AM Representative Hour Overall Intersection and Approach LOS Summary ................................................................................................................................................. 9-81

Figure 9.30: 2040 Preferred Alternative AM Representative Hour Overall Intersection and Approach LOS Summary ...................................................................................................................................... 9-81

Figure 9.31: 2040 Preferred Alternative, 2040 No-Build, and Existing PM Travel Time Comparison – I-66 Westbound ...................................................................................................................................... 9-84

Figure 9.32: 2040 Preferred Alternative, 2040 No-Build, and Existing PM Travel Time Comparison – I-66 Eastbound ....................................................................................................................................... 9-86

Figure 9.33: 2040 Preferred Alternative PM Peak Period Speed Comparison – I-66 Westbound General Purpose Lanes ........................................................................................................................ 9-88

Figure 9.34: 2040 Preferred Alternative PM Peak Period Speed Comparison – I-66 Eastbound General Purpose Lanes ..................................................................................................................................... 9-89

Figure 9.35: Summary of 2040 PM Representative Hour Segment Densities ..................................... 9-95

Figure 9.36: 2040 PM Representative Hour Summary of Vehicle Densities ....................................... 9-96

Figure 9.37: 2040 No-Build PM Representative Hour Intersection LOS Summary ........................... 9-103

Figure 9.38: 2040 Preferred Alternative PM Representative Hour Intersection LOS Summary ........ 9-104

Figure 9.39: Haymarket Park-and-Ride I-66 Express Lane Ramps ................................................... 9-106

Figure 9.40: University Boulevard at I-66 Express Lane Ramps * ..................................................... 9-107

Figure 9.41: Route 234 Bypass Park-and-Ride I-66 Express Lane Ramps ....................................... 9-108

Figure 9.42: Balls Ford Road Park-and-Ride I-66 Express Lane Ramps .......................................... 9-109

Figure 9.43: Braddock Road at Route 28 ........................................................................................... 9-110

Figure 9.44: Stringfellow Road at I-66 Express Lane Ramps ............................................................ 9-111

Figure 9.45: Monument Drive at I-66 Express Lane Ramps .............................................................. 9-112

Figure 9.46: US 50 at I-66 Express Lane Ramps .............................................................................. 9-113

Figure 9.47: Route 123 at I-66 Express Lane Ramps ........................................................................ 9-114

Figure 9.48: Vaden Drive at I-66 Express Lane Ramps ..................................................................... 9-115

Figure 9.49: University Boulevard and I-66 Express Lanes (Phase 1 and Preferred Alternative) ..... 9-117

Figure 9.50: Westfield Boulevard and Stonecroft Boulevard ............................................................. 9-118

Figure 9.51: Monument Drive and I-66 Express Lanes (Phase 1) ..................................................... 9-119

Figure 9.52: Route 123 and Eaton Place ........................................................................................... 9-120



Tables

Table ES.1: Overall Performance Comparison for 2040 AM No-Build and Preferred Alternative ........... vii

Table ES.2: Overall Performance Comparison for 2040 PM No-Build and Preferred Alternative .......... viii

Table 5.1: Communities Served by the Proposed Project ..................................................................... 5-1

Table 7.1: Design Parameters ................................................................................................................ 7-1

Table 8.1: Travel Demand Modeling Assumptions ................................................................................ 8-1

Table 8.2: Traffic Volume Estimation Steps ........................................................................................... 8-4

Table 8.3: Traffic Volume Post-Processing Assumptions ...................................................................... 8-5

Table 9.1: Existing Conditions AM Intersections with LOS E or LOS F (7:00 – 8:00 a.m.) ................. 9-13

Table 9.2: Existing Conditions PM Intersections with LOS E or LOS F (4:30 – 5:30 p.m.) ................. 9-20

Table 9.3: Congested Basic Freeway Segments, 2025 No-Build AM – I-66 Eastbound ..................... 9-31

Table 9.4: Congested Basic Freeway Segments, 2025 Phase 1 Alternative AM – I-66 Eastbound... 9-31

Table 9.5: Congested Weave Freeway Segments, 2025 No-Build AM – I-66 Eastbound ................... 9-32

Table 9.6: Congested Weave Freeway Segments, 2025 Phase 1 Alternative AM – I-66 Eastbound . 9-32

Table 9.7: Congested Ramp Junction Freeway Segments, 2025 No-Build AM – I-66 Eastbound ...... 9-33

Table 9.8: 2025 AM Ramps Where Average Queues Exceed Available Storage ............................... 9-39

Table 9.9: 2025 No-Build and Phase 1 Alternative AM Intersections with LOS E or F (7:00 – 8:00 a.m.) . ................................................................................................................................................. 9-40

Table 9.10: Congested Basic Freeway Segments, 2025 No-Build PM – I-66 Westbound .................. 9-50

Table 9.11: Congested Basic Freeway Segments, 2025 No-Build PM – I-66 Eastbound ................... 9-50

Table 9.12: Congested Weave Freeway Segments, 2025 No-Build PM – I-66 Westbound ................ 9-51

Table 9.13: Congested Ramp Junction Freeway Segments, 2025 No-Build PM – I-66 Westbound ... 9-51

Table 9.14: Congested Ramp Junction Freeway Segments, 2025 No-Build PM – I-66 Eastbound .... 9-52

Table 9.15: 2025 PM Ramps Where Average Queues Exceed Available Storage ............................. 9-58

Table 9.16: 2025 No-Build and Phase 1 Alternative PM Intersections with LOS E or F (4:30 – 5:30 p.m.) ................................................................................................................................................. 9-59

Table 9.17: Congested Basic Freeway Segments, 2040 No-Build AM – I-66 Eastbound ................... 9-69

Table 9.18: Congested Basic Freeway Segments, 2040 Preferred Alternative AM – I-66 Eastbound 9-69

Table 9.19: Congested Basic Freeway Segments, 2040 No-Build AM – I-66 Westbound .................. 9-70

Table 9.20: Congested Weave Freeway Segments, 2040 No-Build AM – I-66 Eastbound ................. 9-70

Table 9.21: Congested Weave Freeway Segments, 2040 Preferred Alternative AM – I-66 Eastbound ... ................................................................................................................................................. 9-71

Table 9.22: Congested Ramp Junction Freeway Segments, 2040 No-Build AM – I-66 Eastbound .... 9-72

Table 9.23: Congested Ramp Junction Freeway Segments, 2040 Preferred Alternative AM – I-66 Eastbound ............................................................................................................................................ 9-72

Table 9.24: Congested Ramp Junction Freeway Segments, 2040 No-Build AM – I-66 Westbound .. 9-73



Table 9.25: 2040 AM Ramps Where Average Queues Exceed Available Storage Comparison of No-Build and Preferred Alternative ............................................................................................................ 9-79

Table 9.26: 2040 AM Intersections with LOS E or LOS F (7:00 – 8:00 a.m.) ...................................... 9-80

Table 9.27: Congested Basic Freeway Segments, 2040 No-Build PM – I-66 Westbound .................. 9-90

Table 9.28: Congested Basic Freeway Segments, 2040 Preferred Alternative PM – I-66 Westbound ..... ................................................................................................................................................. 9-90

Table 9.29: Congested Basic Freeway Segments, 2040 No-Build PM – I-66 Eastbound ................... 9-91

Table 9.30: Congested Basic Freeway Segments, 2040 Preferred Alternative PM – I-66 Eastbound ...... ................................................................................................................................................. 9-91

Table 9.31: Congested Weave Freeway Segments, 2040 Preferred Alternative PM – I-66 Westbound .. ................................................................................................................................................. 9-92

Table 9.32: Congested Weave Freeway Segments, 2040 Preferred Alternative PM – I-66 Eastbound .... ................................................................................................................................................. 9-92

Table 9.33: Congested Ramp Junction Freeway Segments, 2040 No-Build PM – I-66 Westbound ... 9-93

Table 9.34: Congested Ramp Junction Freeway Segments, 2040 Preferred Alternative PM – I-66 Westbound ........................................................................................................................................... 9-93

Table 9.35: Congested Ramp Junction Freeway Segments, 2040 No-Build PM – I-66 Eastbound .... 9-94

Table 9.36: Congested Ramp Junction Freeway Segments, 2040 Preferred Alternative PM – I-66 Eastbound ............................................................................................................................................ 9-94

Table 9.37: 2040 PM Ramps Where Average Queues Exceed Available Storage ........................... 9-101

Table 9.38: 2040 PM Intersections with LOS E or LOS F (4:30 – 5:30 p.m.) .................................... 9-102

Table 9.39: Overall Performance Comparison for 2025 AM No-Build and Phase 1 Alternative ........ 9-121

Table 9.40: Overall Performance Comparison for 2025 PM No-Build and Phase 1 Alternative ........ 9-122

Table 9.41: Overall Performance Comparison for 2040 AM No-Build and Preferred Alternative ...... 9-123

Table 9.42: Overall Performance Comparison for 2040 PM No-Build and Preferred Alternative ...... 9-124

Table 10.1: Quantitative Safety Analysis Summary ............................................................................. 10-3

Table 10.2: Interstate Mainline Crash Hot-Spot Location .................................................................... 10-7

Table 10.3: Interstate Mainline Crash Hot-Spot Locations by Crash Type .......................................... 10-9

Table 10.4: Interstate Crash Rate Summary ...................................................................................... 10-10

Table 10.5: Freeway Safety Analysis Zone Crash Rate Summary .................................................... 10-10

Table 10.6: 2011 ISATe Predicted Crash Frequency Summary ........................................................ 10-12

Table 10.7: 2011 ISATe Potential for Safety Improvement (PSI) Summary ...................................... 10-13

Table 10.8: 2011 Arterial HSM Predicted Crash Frequency Summary ............................................. 10-14

Table 10.9: 2011 Arterial HSM Potential for Safety Improvement (PSI) Summary ............................ 10-14

Table 10.10: 2011 Arterial Potential for Safety Improvement (PSI) Intersection Hot Spots .............. 10-16

Table 10.11: 2011 Arterial Potential for Safety Improvement (PSI) Segment Hot Spots ................... 10-17

Table 10.12: Freeway (ISATe) Predicted Crash Frequency Summary – 2040 No-Build ................... 10-19



Table 10.13: Arterial HSM 2040 No-Build Predicted Crash Frequency Summary............................. 10-20

Table 10.14: Preferred Alternative Freeway (ISATe) Predicted Crash Comparison by Safety Analysis Zone ............................................................................................................................................... 10-22

Table 10.15: Arterial 2040 No-Build and Preferred Build Comparison .............................................. 10-23

Table 10.16: HSM Predicted Crash Comparison by Arterial Analysis Zones .................................... 10-24

Table 11.1: Summary of Land Use Related Effects ............................................................................. 11-8

Table 11.2: Consistency with Plans and Policies ................................................................................. 11-8

Table 12.1: Summary of Environmental Resources ............................................................................. 12-1

Table 12.2: Summary of Environmental Impacts ................................................................................. 12-4

Table 12.3: Present and Reasonably Foreseeable Future Actions ..................................................... 12-7

Exhibits (In separate volume)

Exhibit 4.1: Study Area

Exhibit 4.2: Study Area (continued)

Exhibit 5.1: Existing Conditions Roadway Network

Exhibit 7.1: Summary of Design Exceptions and Design Waivers

Exhibit 7.1: Summary of Design Exceptions and Design Waivers

Exhibit 10.1: I-66 Safety Zones I-66 Mile Markers 38.5 to 53.5

Exhibit 10.1b: I-66 and I-495 Safety Zones I-66 Mile Markers 53.5 to 67.0

Exhibit 10.2: Interstate Mainline Crash Hot Spot Location

Exhibit 10.3: Example Crash Density Map – Interstate Mainline

Exhibit 10.4: Example Crash Density Map – Arterial

Exhibit 10.5: Crash Rates by Safety Analysis Zones

Exhibit 10.6: I-66 and I-495 Safety Zone ISATe Predicted Crashes Analysis Summary – Existing (2011)

Exhibit 10.7:Example ISATe Predicted Crash Analysis – Existing (2011)

Exhibit 10.8: I-66 and I-495 Safety Zone ISATe PSI Analysis Summary – Existing (2011)

Exhibit 10.9: Example ISATe PSI Analysis– Existing (2011)

Exhibit 10.10: I-66 and I-495 Arterial Safety Analysis Zone HSM Spreadsheet Summary – KABC Predicted Crashes – Existing (2011-2013)

Exhibit 10.11: I-66 and I-495 Arterial Safety Analysis Zone HSM Spreadsheet Summary – PDO Predicted Crashes – Existing (2011-2013)

Exhibit 10.12: I-66 and I-495 Arterial Safety Analysis Zone HSM Spreadsheet Summary – KABC PSI – Existing (2011)

Exhibit 10.13: I-66 and I-495 Arterial Safety Analysis Zone HSM Spreadsheet Summary – PDO PSI – Existing (2011)

Exhibit 10.14: I-66 and I-495 Freeway ISATe Safety Analysis Summary– Predicted Crashes – No-Build (2040)



Exhibit 10.15: Example Freeway (ISATe) Analysis – Predicted Crashes – No-Build (2040)

Exhibit 10.16: I-66 and I-495 Arterial Safety Analysis Zone HSM Spreadsheet Summary – KABC Predicted Crashes – 2040 No-Build

Exhibit 10.17: I-66 and I-495 Arterial Safety Analysis Zone HSM Spreadsheet Summary – PDO Predicted Crashes – 2040 No-Build

Exhibit 10.18: Summary I-66 and I-495 Freeway Safety Zone (ISATe) Analysis – Predicted Crashes – Build (2040)

Exhibit 10.19: Route 28 Freeway Safety Zone (ISATe) Analysis – Predicted Crashes – Build (2040)

Exhibit 10.20: Summary I-66 and I-495 Arterial Safety Zone (HSM Spreadsheet) Analysis – KABC Predicted Crashes – Build (2040)

Exhibit 10.21: Summary I-66 and I-495 Arterial Safety Zone (HSM Spreadsheet) Analysis – PDO Predicted Crashes – Build (2040)


Transform 66 Outside the Beltway i

EXECUTIVE SUMMARY

ES.1 Project Background Interstate 66 (I-66) was developed to serve east-west travel between Washington, DC, and I-81 near Strasburg, Virginia. Initial planning for the 76-mile corridor began in 1956, and the first segments west of I-495 were opened between 1958 and 1964. Since its initial construction, access and capacity along the interstate west of I-495 have been expanded numerous times. Despite these infrastructure improvements, population and employment growth in Fairfax and Prince William Counties has steadily increased demand for travel on I-66 and its parallel routes, resulting in congested conditions, especially during weekday commute periods.

I-66 travels through the counties of Fairfax and Prince William and varies in geometry and operations over the 25-mile study corridor. At the western limits of the study area, two general purpose lanes are provided in each direction between US 15 and US 29 (Gainesville). A VDOT widening project is underway and will provide improvements resulting in three general purpose lanes and one high-occupancy vehicle (HOV) lane in each direction by 2016. Near the US 29 (Gainesville) interchange, the roadway widens, providing three general purpose lanes and one HOV lane in each direction. HOV restrictions are in place on weekdays for 2.5 hours in the peak direction of travel. Outside the hours of enforcement, the HOV lane is open to all traffic. At the US 50 interchange, the number of continuously operational travel lanes is reduced to two general purpose lanes and one HOV lane. The outside shoulder lane functions as a third general purpose lane on weekdays for a limited period of time in the peak direction of travel. East of the I-495 interchange, the number of travel lanes is reduced to two lanes in each direction. In the peak direction of travel, I-66 east of I-495 is restricted as an HOV-only facility on weekdays.

The Virginia Department of Transportation (VDOT) and the Virginia Department of Rail and Public Transportation (DRPT), in cooperation with the Federal Highway Administration (FHWA), propose to make the following changes to the I-66 corridor outside the Beltway:

Provide three general purpose lanes in each direction along the entire 25-mile corridor; Construct two continuously operating Express Lanes in each direction that would be separated by

flexible delineator posts and provide alternative travel options for toll paying customers, HOV users with 3 or more occupants (exempt from tolls), and commuter bus service; and

Construct direct or nearly direct access between the Express Lanes and new or expanded park-and-ride facilities.

ES.1.1 Project Termini Federal Highway Administration (FHWA) regulations implementing the National Environmental Policy Act (NEPA) require that the action evaluated in each Environmental Impact Statement (EIS) or Environmental Assessment (EA) and Finding Of No Significant Impact (FONSI) shall:

1. Connect logical termini and be of sufficient length to address environmental matters on a broad scope;

2. Have independent utility or independent significance, i.e., be usable and be a reasonable expenditure even if no additional transportation improvements in the area are made; and

3. Not restrict consideration of alternatives for other reasonably foreseeable transportation improvements.


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The central basis of all three of the above criteria is that projects have rational end points. Considering these requirements, the I-66 Corridor Improvements Project identified the western project terminus as US 15 and the eastern project terminus as I-495.

The Preferred Alternative identified in the EA and selected in the FONSI includes a program of multimodal improvements between Haymarket and I-495. A subset of the Preferred Alternative was developed and is identified in this Interchange Justification Report (IJR) as Phase 1, which provides for a phased approach to delivering the Preferred Alternative, and includes Express Lanes for 22 of the Project’s 25 miles, from Gainesville to I-495. The Department is procuring a private Developer through the Virginia Office of Public Private Partnerships (VAP3) to design, build, own, and operate the I-66 Express Lanes, and to implement Phase 1. The analysis of the proposed action included in this IJR, for the design year 2040, is based on the Preferred Alternative as noted in the EA. Proposed improvements that are to be constructed in Phase 1 are analyzed in this study for an interim year of 2025:

Phase 1 (interim analysis year 2025) – approximately 22 miles of improvements between US 29 (Gainesville) and I-495, considering select elements of the Preferred Alternative.

Preferred Alternative (design analysis year 2040) – approximately 4 miles of additional improvements between US 15 and US 29 (Gainesville), along with additional access to/from the Express Lanes at Route 234 Bypass/Cushing Road Park and Ride Lot, and enhanced access at Stringfellow Road and Monument Drive.

Phase 1 improvements were developed to implement the critical infrastructure improvements identified in the Preferred Alternative necessary to provide the intended access and free-flow operations within the I-66 Express Lanes. Given the significant cost to implement the full range of improvements identified in the Preferred Alternative, the Phase 1 improvements are also considered to be more cost effective and feasibly constructible in the near term. As part of the proposed Phase 1 improvements, three general purpose and two Express Lanes will be constructed. Access to/from the Express Lanes and the intersecting arterial roadways will be provided at eight locations between University Boulevard and Vaden Drive. To reduce arterial roadway impacts at service interchange locations, existing bridge infrastructure will remain in its existing condition with new or modified ramp terminals constructed up to the arterial intersection. These limited arterial modifications, in conjunction with the reduction in I-66 improvements from 25 to 22 miles, represent the greatest cost savings to the project.

Right-of-way (ROW) for proposed improvements of the Preferred Alternative are identified as part of the Tier 2 NEPA study. Only the ROW required for Phase 1 will be acquired at this time. One component of the Preferred Alternative not considered in Phase 1 is the complete preservation of right-of-way in the median of I-66 for future transit expansion. This requires the reconfiguration of Express Lanes access provided under Phase 1 at Stringfellow Road and Monument Drive. The Preferred Alternative also includes the widening of the I-66 overpass at US 29 (Centreville), which is not included in Phase 1 as a means of mitigating potential impacts to existing ROW. In addition to these elements, in the Preferred Alternative, the Express Lanes are extended to US 15 and direct access is provided at the Route 234 Bypass from the Cushing Road park-and-ride lot and a future intersecting roadway west of US 15.

ES.1.2 Summary of Project Purpose and Need The purpose of this study is to address existing and future transportation operations on I-66. The study evaluates the effectiveness of both highway and transit improvements in meeting the identified needs. The identified needs to be addressed include the following:

Transportation Capacity Deficiencies – existing travel demands in the corridor exceed the


Transform 66 Outside the Beltway iii

carrying capacity of I-66. Growth in the corridor is anticipated to further increase future travel demand, resulting in additional congestion and crowding both in terms of locations and duration.

Major Points of Congestion – there are a number of specific constraints (chokepoints) where congestion is particularly significant for traffic and transit operations.

Limited Travel Mode Choices – transit is principally limited to peak periods in the peak direction, with very little transit service offered during off-peak periods in off-peak directions; limited accommodations for bicycling and walking are provided within the corridor.

Safety Deficiencies – several areas within the corridor have high crash rates compared to the I-66 corridor average.

Lack of Transportation Predictability – travelers experience highly unreliable travel times on I-66, in both the general purpose and HOV lanes, particularly during peak periods, although not uncommon outside of peak periods and on weekends, which adversely affects both travel times and service predictability for the bus services that make use of the I-66 roadway.

ES.2 Summary of Proposed Action Under the proposed action for this IJR, the following improvements are proposed as part of the I-66 Corridor Improvements Project:

Reconfigure the existing HOV lanes and construct approximately 25+ miles of Express Lanes between US 15 and I-495 (two lanes in each direction) for the Preferred Alternative (by year 2040); for Phase 1, the Express Lanes will be constructed between east of US 29 in Gainesville and I-495, with the remaining 4 miles from Gainesville to US 15 operating as a single HOV lane;

Reconfigure the existing general purpose lanes to provide three general purpose lanes in each direction with auxiliary lanes connecting most system interchanges; and

Construct direct or nearly direct access between the Express Lanes and new or expanded park-and-ride facilities.

In addition to access provided to and from arterial roadways and park-and-ride facilities, intra-system access will be provided along I-66 between the Express Lanes and general purpose lanes at four key locations:

Westernmost terminus of the project at US 15 (Preferred Alternative by 2040); Under Phase 1, the westernmost access point will be just east of US 29 in Gainesville.

In the vicinity and east of the Route 28 interchange (at-grade slip ramps for entry, directional flyovers for exit).

Between Route 243 (Nutley Street) and I-495 in the eastbound direction only (directional flyover for entry, allowing access from the I-66 general purpose lanes to the I-66 Express Lanes before they connect with the I-495 Express Lanes).

Easternmost terminus of the project past I-495.

Other infrastructure elements associated with the project would include signage, electronic variable message displays, electronic toll collection equipment, trail, sound barrier walls, and stormwater management facilities.


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ES.3 Summary of Findings The operational and safety analysis performed as part of the access request includes the general purpose and Express Lanes, associated ramps and collector-distributor (C-D) roads for the length of the project, plus adjacent interchanges to the west (Old Tavern Road) and east (Route 7, Dulles Toll Road) of the I-66 study area. The first interchange to the north and south of I-66 was also considered along Route 28 and Fairfax County Parkway. At each of the interchanges, the crossroads included the ramp terminal intersections and adjacent local street intersections (within close proximity). At I-495 at least one interchange to the north and south of I-66 was included in the analysis.

The proposed plan should produce marked operational improvements to the overall system by increasing capacity of and directing access to the flexible-post bollard-separated Express Lanes in contrast to the existing conditions of a concurrent, non-separated HOV lane. The improvements should also demonstrate operational benefits by transferring some of the traffic currently using the over-saturated general purpose lanes to the proposed Express Lanes, which will have greater capacity and operational performance than the current single HOV lane. The analysis using traffic simulation software showed improvements in travel times, throughput, speeds, and congestion/queuing on a number of segments within the general purpose lanes without degrading operations within the proposed Express Lanes, which will operate at a free-flow speed of 45 mph or greater. A detailed assessment of traffic operations using microsimulation (VISSIM) is presented in Chapter 9 of this document.

ES.3.1 Operational Analysis Findings Traffic operational analyses and quantitative safety studies consistent with FHWA’s policy are documented herein. Existing 2015 analyses demonstrate the need for corridor-wide improvements to mitigate recurring congestion. Weekday mainline operations on I-66 consist of sustained congestion and reduced travel speeds in the peak direction of travel (eastbound in the AM peak period, westbound in the PM peak period). Major points of congestion include the Route 234 Business, Route 28, US 50, and I-495 interchanges. Arterial degradation is also exhibited along Route 28, US 50, Route 123, and Route 243 (Nutley Street), with as much as 25 percent of the study area intersections operating at level of service (LOS) E or worse.

The traffic operational analyses show marked improvements between the No-Build and Build conditions in 2025 and 2040. Route 28, a bottleneck during both peak periods today, has planned improvements to expand capacity in the No-Build condition along Route 28. However, at-grade signalized intersections will remain, and the current interchange configuration is inadequate based upon forecast demand, resulting in worsened peak period congestion. Both in Phase 1 and in the Preferred Alternative, the proposed I-66 improvements to the Route 28 interchange and additional arterial capacity help to relieve congestion through the interchange in 2025 and 2040. This results in significant reductions in vehicle density and increased travel speeds through the interchange in the general purpose lanes, contributing to overall reductions in corridor travel times.

Overall, the results from the traffic analysis of Phase I and Preferred Alternative improvements show that the entire corridor experiences significant operational improvements in the peak direction for both the AM and the PM peak periods. The improvements carry more demand volume at higher speeds and lower density than those of the No-Build scenario. One of the reasons the Preferred Alternative is anticipated to carry more demand volume is the additional capacity added by the Express Lanes, when compared to the capacity of the No-Build condition. Nevertheless, some areas of congestion still remain in the corridor on the general purpose lanes.


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Congestion during the AM peak period in Phase 1 consists of limited segments and durations of moderate to severe congestion, which are primarily attributed to the Route 123 interchange bottleneck. Heavy weaving volumes between the US 50 and Route 243 (Nutley Street) interchanges results in a breakdown in network operations through most of the peak period. Additionally, in Phase 1, very little congestion is expected in the peak direction of travel during the PM peak period, with areas of heavy congestion limited to segments east of the I-495 interchange.

Similarly in the Preferred Alternative, while the overall operational improvements for the project are noteworthy in terms of greater demand served, higher speeds, and lower densities, the continued growth along the corridor and increase in travel demand results in greater congestion in certain areas during the peak periods. Severe congestion is expected through a good portion of the AM peak period between Route 28 and Route 123, with shorter durations of severe congestion as far east as Route 243 (Nutley Street) and as far west as Route 234 Business. Capacity improvements along I-66 and Route 28 allow for greater throughput approaching the US 29 (Centreville) interchange during the PM peak period. However, the Manassas Battlefield to the north of I-66 hinders expansion west of US 29 (Centreville), the result of which limits the number of general purpose lanes to three in each direction without auxiliary lanes. This causes congestion for most of the PM peak period at the US 29 (Centreville) interchange, the extent of which escalates through the PM peak period to reach the Route 243 (Nutley Street) interchange by the end of the peak period.

Aside from these examples, all other instances of reduced travel speeds within the general purpose lanes are isolated and occur for short durations during the peak period. Overall, the Preferred Alternative eases corridor-wide congestion as measured by vehicle density along freeway mainline, ramp, and weave segments. During the AM peak period, the number of congested freeway segments is reduced by half from 60 percent in the No-Build to 30 percent in the Preferred Alternative. During the PM peak period, a similar reduction of approximately 50 percent compared to the No-Build condition is expected in the Preferred Alternative, with only 27 percent of freeway segments operating in a congested condition. Supporting documentation also includes a functional signing plan (Appendix E) and assumptions used in developing a signing concept, as provided in Section 13 of this document.

ES.3.2 Crash Analysis Findings Planning-level crash analyses were performed using industry standard practice and highway safety analysis tools. Crash data was compiled for freeway segments along I-66 (US 15 to the Dulles Toll Road) and I-495 (Gallows Road to Route 7) for the period between January 2011 and December 2013. Crash data was also compiled during the same time period at existing and future interchange locations. The analysis of the crash data evaluated the safety performance of the existing condition and assessed the differences between the 2040 No-Build and Build alternatives. Both qualitative and quantitative analyses were conducted to evaluate existing, No-Build, and Preferred Alternative Build conditions in the I-66 corridor. The safety analyses focused on the network as a system, including mainline segments, ramps, collector-distributor roads, intersections, and arterials.

The results of the safety analysis showed that the highest crash frequencies (both existing and predicted) in the study area occurred in the vicinity of the entrance and exit ramps at the interchanges along the mainline. Additionally, the magnitude of crashes was higher between the US 29 (Centreville) and the I-495/I-66 interchanges. These higher crash frequencies were attributed primarily to the higher traffic congestion and geometric restrictions.

Despite the increased crash frequency, there was no strong indication that the severity of crashes differed along the corridor in relation to the increased frequency. While there were select areas where


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crash frequency peaked (hot spots), the severity was fairly consistent throughout the corridor. This can be attributed to the decreased speed associated with the congestion in the corridor. While increased crash frequency can be directly attributed to the increase in traffic volumes, the relatively low speeds that are associated with congested conditions can limit and, in some cases, reduce the severity of crashes.

Based on the total predicted crashes, the most critical safety sections along I-66 under No-Build conditions are expected to be between the Route 123 and Route 243 (Nutley Street) interchanges and at the I-66/I-495 interchange. The same section of roadway is projected to operate with improved safety under 2040 Build conditions. The 5-mile section of I-66 yielded the top three interchanges, Fairfax County Parkway, US 50 and Route 123, when comparing the predicted crashes for 2040 No-Build and the Preferred Alternative. For the Preferred Build Alternative, analyses were also completed for a total of 5.3 miles of arterials and 29 intersections. The arterial study area (including the safety impacts of segments and intersections) with the highest number of predicted crashes per year was at the Route 234 Bypass.

Overall, an improvement in safety conditions is expected along the I-66 corridor under the Preferred Alternative as compared to the No-Build condition. The most critical safety locations will continue to be the areas with the highest traffic volumes between the Fairfax County Parkway and I-495. As the project continues into detailed design or where potential design exceptions are evaluated, consideration should be given to areas identified as hot spots as well as the future safety considerations outlined in Section 10.7.

ES.4 Conclusions The proposed improvements outlined in this IJR satisfy the recommendations set forth by the FHWA in the Tier 1 Final Environmental Impact Statement (FEIS) Record of Decision (ROD). The provision for three general purposes lanes in each direction accommodates non-HOV travelers, with the additional capacity of two Express Lanes in each direction providing a more reliable transportation option for HOV travelers as well as toll paying customers. The Express Lanes also provide at or nearly direct access to park-and-ride facilities and transit. Modifications to system interchanges and construction of auxiliary lanes between many adjacent interchanges address sources of congestion while enhancing the safety of operations. Overall, the Preferred Alternative provides a notable improvement in operations as compared to the No-Build condition, does not diminish the safety of freeway, interchange, or arterial operations, and allows for median-run transit expansion in the future.

This report demonstrates that the Preferred Alternative is consistent with the eight policy points in Chapter 3 under the FHWA’s Policy on Access to the Interstate System. An overall performance comparison for the Preferred Alternative with No-Build is presented in Tables ES.1 and ES.2. VDOT supports this Preferred Alternative as addressing the fundamental issues and concerns presented in this document and in the EA, and formally requests that the FHWA find this plan to be geometrically and operationally acceptable.


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Table ES.1: Overall Performance Comparison for 2040 AM No-Build and Preferred Alternative

Measure of Effectiveness

Description Units 2040 AM No-Build

Value

2040 AM Pref. Alt.

Value

Pref. Alt. Performance

Compared to No-Build

Travel Time – General Purpose

Measured for the entire corridor in the EB direction, from Old Tavern Rd to Dulles Toll Road

Minutes 90 53

Travel Time – HOV/Express Lanes


Minutes 46 32

Number of Main Bottlenecks

Locations along the corridor in the EB direction where traffic volumes are heavily constrained generating upstream congestion

Number 5 2

Average Volume Throughput

Average for all measures taken at screenline locations along the corridor and in the EB direction. Includes both general purpose and HOV/Express Lanes volumes

Veh/hr 6,100 9,100

Average Persons Moved

Average for five screenline locations taken along the corridor in the EB direction. Includes vehicular, bus transit, and rail transit riders

Persons/hr

10,700 14,300

Average Un-served Demand

Average for all measures taken at screenline locations along the corridor and in the EB direction. Includes both general purpose and HOV/Express Lanes demand

% 21 7

Intersections at LOS E and F

Summary for all intersections within the study area

% 12 17

Basic Freeway Segments Congested – General Purpose

Summary for all basic segments along the corridor and in the EB direction

Number 20 14

Weave Segments Congested – General Purpose

Summary for all weaving segments along the corridor and in the EB direction

Number 4 1

Ramp Junctions Congested – General Purpose

Summary for all merge and diverge segments along the corridor and in the EB direction

Number 14 10

Note: Calculations in this table were based upon the distance between Old Tavern Road and Dulles Toll Road, approximately 36 miles.

Better < < < < > > > > Worse


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Table ES.2: Overall Performance Comparison for 2040 PM No-Build and Preferred Alternative


Description Units 2040 PM No-Build

Value

2040 PM Pref. Alt.

Value




Measured for the entire corridor in the WB direction, from Dulles Toll Road to Old Tavern Rd

Minutes 66 44



Minutes 45 32


Locations along the corridor in the WB direction where traffic volumes are heavily constrained generating upstream congestion

Number 4 1


Average for all measures taken at screenline locations along the corridor and in the WB direction. Includes both general purpose and HOV/Express Lanes volumes

Veh/hr 6,300 8,900


Average for five screenline locations taken along the corridor in the WB direction. Includes vehicular, bus transit, and rail transit riders

Persons/hr

11,900 15,100


Average for all measures taken at screenline locations along the corridor and in the WB direction. Includes both general purpose and HOV/Express Lanes demand

% 17 10



% 36 19

Basic Freeway Segments Congested

Summary for all basic segments along the corridor and in the WB direction

Number 12 7


Summary for all weaving segments along the corridor and in the WB direction

Number 0 3


Summary for all merge and diverge segments along the corridor and in the WB direction

Number 16 8

Note: Calculations in this table were based upon the distance between Old Tavern Road and Dulles Toll Road, approximately 36 miles

Better < < < < > > > > Worse


Transform 66 Outside the Beltway 1-1

CHAPTER 1. BACKGROUND

1.1 Proposed Tier 2 Action The Virginia Department of Transportation (VDOT) and the Virginia Department of Rail and Public Transportation (DRPT), in cooperation with the Federal Highway Administration (FHWA), Fairfax County, Town of Vienna, City of Fairfax, and Prince William County, evaluated improvement alternatives for the I-66 corridor from US 15 in Prince William County to I-495 in Fairfax County. The development of improvements in this corridor followed a tiered National Environmental Policy Act (NEPA) process. The Tier 1 Final Environmental Impact Statement (FEIS) was completed in November 2013, and FHWA issued a Record of Decision (ROD) on November 20, 2013, concurrent with publication of the Tier 1 FEIS.

As stated in the Tier 1 ROD, the transportation needs in this corridor cannot be met with a single, standalone improvement concept; rather, a combination of improvements will be necessary, some of which can be implemented in the near term, while others can be realized over a longer term. Because all of these improvements cannot be implemented simultaneously, the tiering process provides for phased implementation of a variety of improvements as independent elements of an overall long-term program of projects. Accordingly, VDOT has used the planning efforts, findings, and decisions from the Tier 1 FEIS to frame the elements of this Tier 2 project, which represents a combination of concepts over the 25-mile-long corridor.

Under the proposed Tier 2 project, I-66 would be improved to provide:

Three regular (general purpose) lanes in each direction. Two managed lanes (also referred to as Express Lanes) in each direction that would support:

o Toll paying customers. o High-occupancy vehicle (HOV) users with three or more occupants exempt from tolls. o High-frequency and quality bus service.

Direct or nearly direct access between the managed lanes and new or expanded park-and-ride facilities.

The above items constitute the I-66 Corridor Improvements Project, also referred to as “Transform 66 Outside the Beltway” (the project). Together, these items will satisfy the following elements from the Tier 1 ROD:

Improving three general purpose lanes and adding auxiliary lanes between interchanges where appropriate.

Repurposing a portion of the right-of-way to provide managed lanes, which should result in consistent travel times for an enhanced transit service, HOV-3 users, and toll-paying customers.

Fixing chokepoints. Addressing safety issues. Enhancing intermodal connectivity with the addition of new park-and-ride facilities, expansion of

existing facilities, enhancement to commuter bus services, new parallel corridor-wide shared use path and sidewalk improvements and investing in travel demand management (TDM) strategies.

Integrating transportation communications and technology.

It should be noted that these elements represent 6 of the 10 elements of the I-66 Tier 1 EIS ROD. One of those 10 elements, the Virginia Railway Express (VRE) extension, is continuing; VRE is in the planning phase for this extension. The remaining three elements of the ROD included dedicated travels ways for



Metrorail, light rail, and/or bus rapid transit. The proposed I-66 Corridor Improvements Project is advancing so as not to preclude a future extension of Metrorail or other major transit investments within the right-of-way.

1.2 Project Development History I-66 was originally developed to serve east-west travel between Washington, DC, and I-81 near Strasburg, Virginia. Initial planning for the 76-mile corridor began in 1956, and the first segments west of I-495 were opened between 1958 and 1964. Since its original construction, access and capacity along the interstate west of I-495 have been expanded numerous times. Despite these infrastructure improvements, growth in Fairfax and Prince William counties has steadily increased demand for travel along I-66 and its parallel routes, resulting in congested conditions, especially during weekday commute periods.

The proposed corridor improvements identified in the Preferred Alternative are consistent with those identified in the Tier 1 Environmental Impact Statement and Tier 1 Record of Decision for Interstate 66 from US Route 15 in Prince William County to Interstate 495 in Fairfax County (Tier 1 EIS and Tier 1 ROD). The Tier 1 EIS and Tier 1 ROD identified 10 “Build” concepts to advance further in the planning process.

The Tier 1 EIS found that the No-Build concept would not meet the needs of the corridor. To meet the corridor’s short- and long-term needs, the Tier 1 EIS found that a combination of Build concepts working in coordination would be needed. Build concepts identified in the Tier 1 EIS consisted of the following:

1. General Purpose Lanes: Construction of additional vehicular travel lanes open to all traffic. 2. Express Lanes: Conversion of the existing high-occupancy vehicle (HOV) lane into a one- or

two-lane (in each direction) facility that would operate as a high-occupancy toll facility where only high-occupancy vehicles would be exempt from paying a toll.

3. Metrorail Orange Line Extension: Metrorail Orange Line extension from Vienna (current western terminus) to Centreville or Haymarket.

4. Light Rail Transit: Light rail transit line extending west from Vienna to either Centreville or Haymarket.

5. Bus Rapid Service: Exclusive bus rapid service extending from the region’s core (or Vienna) to Centreville or Haymarket.

6. Virginia Railway Express (VRE) Extension: Extension of the existing Manassas Line of VRE from Manassas to Haymarket or Gainesville.

7. Spot Capacity Improvements: Improvements to address specific operational issues at specific locations in the I-66 corridor. These could include interchanges, segments or spots along the I-66 mainline, shoulders, merges, diverges, or weaving areas.

8. Safety Improvements: Improvements to address safety issues at specific locations along the corridor and corridor-wide safety concerns (such as lack of adequate and continuous shoulders).

9. Transportation Communication and Technology: Continued enhancements to Intelligent Transportation Systems (ITS) technology for all transportation modes in the corridor, including traveler information, corridor and incident management, and transit technology.

10. Integrated Corridor Management: Integration among a full range of travel modes and technology within the corridor to optimize operations and efficiency in the context of constrained physical modifications to the corridor.

The Tier 1 ROD provides information for initiating a Tier 2 Environmental Analysis for the I-66 study corridor that further explores a combination of the above 10 Build concepts. Accordingly, VDOT initiated a



Tier 2 Environmental Assessment (EA) to explore a set of improvements to I-66, including provisions of additional general purpose lanes, Express Lanes, and rapid bus services on the Express Lanes. The EA also examined modifications to existing interchanges and/or new access/egress points, resulting in the development of this Interchange Justification Report (IJR).

1.3 Relationship to Other Highway Improvement Plans/Programs A number of other studies are taking place that would have an effect on the completion of the freeway and arterial analyses completed as part of this IJR. The following studies have been initiated to support the further development and documentation of specific infrastructure and operations recommendations for the I-66 Corridor Improvements Project:

Tier 2 Environmental Assessment, VDOT. This study developed the scope/specifics of the improvements to meet the needs of the study corridor and documented the impacts of proposed modifications to I-66 as a part of the I-66 Corridor Improvements Project.

Corridor Study Transportation Technical Report (TTR) and Systemwide IJR, VDOT. The IJR (supported by the more detailed study in the TTR) requests approval for new and modified interstate access associated with corridor improvements related to general purpose lanes, express lanes, and transit facilities.

Transit/Transportation Demand Management (TDM) Study, DRPT and VDOT. This study documents transit demand and facility and service needs as inputs to the I-66 Corridor Improvements Project.

Alternatives Development Technical Report, VDOT. This study documents development of alternatives and preliminary engineering (functional level) plans of infrastructure and facility modifications to support defined corridor needs.

Traffic and Revenue Study, Virginia P3 Office. This study documents traffic and revenue forecasts associated with express lane operations along I-66, in coordination with improvements along the general purpose lanes, as part of the I-66 Corridor Improvements Project.

Transform 66 – Inside the Beltway Project (Categorical Exclusion and Transportation Technical Report), VDOT and DRPT. Under a multi-agency partnership, VDOT, DRPT and Northern Virginia Transportation Commission (NVTC) are developing a multimodal program of projects in and around the I-66 corridor from I-495 to US 29 in Rosslyn. For the purposes of the I-66 Corridor Improvements Project (Outside the Beltway), the following assumptions are being used regarding the I-66 Inside the Beltway project:

- HOV-2 to HOV-3 conversion by 2020 with HOV-3+ vehicles traveling free of cost. - Heavy vehicles prohibited and clean fuel vehicles/Dulles International Airport/Off-Duty

Law Enforcement subject to HOV restrictions. - Tolling in both directions during the AM and PM peak periods only (with same 4-hour

restricted period as Outside the Beltway project) with congestion-based toll prices to manage demand.

- VDOT operates and maintains facility. Route 28/I-66 Northern Project. The I-66 Corridor Improvements Project has absorbed the

Route 28 project that includes the Poplar Tree Road/Stonecroft Boulevard Overpass, the removal of the Ellanor C. Lawrence Park entrance traffic signal along Route 28, the extension of Poplar Tree Road from its existing terminus east of Route 28 to Stonecroft Boulevard, and associated improvements at the Westfields Boulevard interchange.



1.4 Support and Commitment from VDOT, Regional, and Local Jurisdictions

Appendix A includes a letter of support from the County of Fairfax Board of Supervisors, dated October 20, 2015. The letter states, “Fairfax County Board of Supervisors endorsed the Recommended Design Concept (Preferred Alternative) for Transforming I-66 Outside the Beltway as recommended and presented by VDOT to the Commonwealth Transportation Board (CTB) on September 15, 2015, contingent upon VDOT’s continued progress toward addressing the comments below regarding the Final Tier 2 Environmental Assessment of the Transforming I-66 Outside the Beltway project, the Preferred Alternative and the phasing of the Preferred Alternative.”

A letter of concurrence from Prince William County, dated August 8, 2016, is included in Appendix A. The letter states, “Prince William County concurs with the new access point modifications as proposed in the Interchange Justification Report. VDOT and Prince William County Department of Transportation have worked in coordination to identify the proposed new access points. The County concurs that the Draft Interchange Justification Report (November 23, 2015 and revised April 2016 to accommodate County staff comments) appropriately documents and demonstrates the operational effectiveness of the proposed new and modified access points.”



CHAPTER 2. PURPOSE AND NEED

2.1 Tier 2 Corridor Needs – Existing Conditions The following existing (2015) conditions within the corridor illustrate the need for improvements:

Nearly half of the corridor’s peak direction roadway miles operate at a Level of Service (LOS) E or worse in the AM representative hour.

Nearly one-third of the corridor’s peak direction roadway miles operate at a LOS E or worse in the PM representative hour.

Peak-period congestion from US 29 (Centreville) to I-495 is 4-5 hours per day (in each direction). The I-66 and I-495 study area corridor crash rates (study years 2011-2013 for injury and property

damage only) are higher than the statewide crash rate averages. Nine specific areas of congestion exist along the corridor near interchanges where geometrics or

capacity constraints cause peak-period delay. There is a lack of traveler information along the corridor that can be used to identify alternate

routes and modes. Many existing park-and-ride lots are at or above capacity and/or lack convenient access to the

I-66 HOV lanes for commuter buses, carpools, and vanpools.

2.2 Tier 2 Corridor Needs – Future Conditions Future conditions will lead to further deteriorating traffic conditions by 2040 as follows:

Traffic is expected to grow 10 percent between US 50 and Route 123 and 78 percent between US 29 (Gainesville) and US 15, adversely affecting both vehicular and transit bus operations.

Employment in the Gainesville-Haymarket area is expected to grow as much as 180 percent. During the AM peak, approximately two-thirds of the study corridor segments in the eastbound

direction are expected to operate at LOS E or LOS F. During the PM peak, over 90 percent of the study corridor segments in the westbound direction

are expected to operate at LOS E or worse in the representative hour. Peak-period congestion in the eastern portion of the corridor is expected to increase to 8-10

hours per day (in each direction), affecting both vehicular operations, as well as the reliability of bus transit services.

The Metrorail Orange Line demand is expected to exceed the capacity of 120 riders per car, even with potential fleet expansion to 100 percent eight-car trains.

The I-66 study corridor is characterized by heavy congestion from commuter traffic during both the morning and evening peak periods, especially in the eastern half of the corridor. In addition to safety challenges caused by this congestion, deficient geometric features create safety impacts in the corridor. These deficient geometric conditions include short acceleration and deceleration lanes and the lack of a shoulder during peak periods. Based on existing analysis, future safety improvement considerations along the I-66 corridor should be focused on Route 123, Route 243, and the I-495 interchanges.

As volumes increase, the nine specific areas of congestion identified along the corridor near interchanges where geometrics or capacity constraints cause peak-period delay will remain and likely worsen.



2.3 Purpose and Need Summary The purpose of this IJR is to address existing and future transportation problems on I-66. The study evaluates the effectiveness of both highway and transit improvements in meeting the identified needs. The identified needs to be addressed include: transportation capacity deficiencies, major points of congestion, limited travel mode choices, safety deficiencies, and lack of transportation predictability.

Transportation Capacity Deficiencies

Travel demands in the corridor, particularly during peak demand periods, exceed the carrying capacity of I-66, many intersecting and parallel routes, and some transit services. Growth in population and employment in the corridor is anticipated to further increase travel demand, resulting in additional congestion and crowding both in terms of locations and duration.

Major Points of Congestion

In addition to the need for increased transportation capacity in the I-66 corridor, traffic and transit operations are adversely affected by specific constraints based on capacity and/or geometric issues. There are a number of specific constraints (chokepoints) where congestion is particularly significant for traffic and transit operations.

Limited Travel Mode Choices

The corridor’s current transit services include the Metrorail Orange Line (to Vienna), commuter and local bus services (principally focused on peak periods), and Virginia Railway Express (VRE) (peak hour, peak direction commuter rail located off-corridor to the south). Though transit is offered throughout most of the corridor, it is principally limited to peak periods in the peak direction. Very little transit service is offered during off-peak periods in off-peak directions. Accommodation is limited for bicycling and walking within the corridor. Continuous parallel bikeways or pedestrian networks do not exist along I-66.

Safety Deficiencies

Based on previous safety evaluations, several areas within the corridor have high crash rates compared to the I-66 corridor average. For example, in both directions of I-66, the areas around the three eastern interchanges have crash rates of more than 100 crashes per hundred million vehicle miles travelled (HMVMT). The high crash rates at these locations are potentially the result of high weaving volumes in the short segment between the two interchanges. Detailed information on crash analysis can be found in Chapter 10 of the IJR.1

Lack of Transportation Predictability

Travelers experience highly unreliable travel times on I-66, particularly during peak periods, although not uncommon outside of peak periods and on weekends. With volumes either at or over capacity, typical travel events such as disabled vehicles and adverse weather conditions can result in substantial variability in travel time. The lack of predictability for travel in the corridor adversely affects the quality of life for travelers in the corridor and also makes it difficult for travelers to make decisions about when to travel and which mode to take. In addition, it adversely affects both travel times and service predictability for the bus services that make use of the I-66 roadway.

1 Tier 1 Environmental Impact Statement and Tier 1 Record of Decision for Interstate 66 from US Route 15 in Prince William County to Interstate 495 in Fairfax County. Virginia Department of Transportation, Virginia Department of Rail and Public Transportation, U.S. Department of Transportation Federal Highway Administration. November 2013.



CHAPTER 3. FHWA INTERSTATE ACCESS POLICY COMPLIANCE

3.1 Responses to FHWA 8-Point Policy on Interstate Highway Access Modifications

The Federal Highway Administration (FHWA) requires the preparation of an Interchange Justification Report (IJR) for every proposed highway system modification that affects Interstate Highway access to facilitate the agency’s independent evaluation of the request and to ensure that alternatives and pertinent factors have been appropriately considered. As the United States Department of Transportation’s final reviewing agency and authority for all Interstate Highway access requests, FHWA has specified eight justification policy points that must be addressed for all requests for new or modified access points to the existing Interstate Highway System. This report addresses each of the eight policy points for the proposed new and modified access points on the Interstate 66 (I-66) corridor between US 15 in Haymarket and I-495.

3.1.1 Policy Point 1: Need for the Access Point Revision The need being addressed by the request cannot be adequately satisfied by existing interchanges to the Interstate, and/or local roads and streets in the corridor can neither provide the desired access, nor can they be reasonably improved (such as access control along surface streets, improving traffic control, modifying ramp terminals and intersections, adding turn bays or lengthening storage) to satisfactorily accommodate the design-year traffic demands.

The I-66 corridor currently experiences significant vehicular congestion during weekday peak commute periods, as well as during multi-hour periods on weekends due to the insufficient capacity of the existing I-66 mainline general purpose and high-occupancy vehicle (HOV) lanes. With continued local and regional population and employment growth, traffic forecasts for the design year (2040) and the interim year (2025) show that, without further investment in I-66, future travel demand will significantly worsen the severity and duration of congestion. The local parallel routes to the I-66 corridor are already operating under congested levels and are being heavily used to bypass I-66. The travel forecasts for 2025 and 2040 show that with the anticipated growth in the region, the local road network along with the I-66 corridor will not have the sufficient capacity to provide reasonable access to the traveling public along this corridor. The local roads that connect to I-66 and provide alternate parallel routes are constrained from further widening, while traffic control and turn-lane improvements are not sufficient to increase the capacity that is needed to address the future demand. Existing I-66 mainline and interchange deficiencies have to be addressed to allow the system (I-66 corridor and local road network) to work with design-year demand.

Along the existing freeway mainline, the leftmost lane is HOV-only during the peak periods (eastbound in the AM and westbound in the PM). This lane, which has no barrier separation from the general purpose lanes, experiences frequent slowdowns due to friction with the general purpose lanes, which are at a standstill in many locations. Additionally, only two existing partial interchanges along the corridor currently provide direct access to the HOV lane (east-facing interchanges at Monument Drive and Stringfellow Road), forcing many HOV users to weave across several lanes of traffic heading to or coming from most interchanges.

The goal of the proposed project is to address existing interchange access points to improve capacity and safety. The proposed project addresses freeway system deficiencies resulting from the access issues and lack of reliability of the HOV lane in addition to the proposed improvements currently identified in the



regional long-range plans. The proposed Express Lanes provide significant improvements to capacity and reliability with direct access from service interchanges, park-and-ride lots, and mainline general purpose lanes. The flexible-post bollards separating the Express Lanes from the general purpose lanes removes friction and prevents weaving between the two facilities. The desired travel speeds on the Express Lanes are maintained by dynamic toll pricing, thus offering reliable travel times to toll-paying customers, HOV-3/vanpools, and buses.

The proposed project also provides a number of improvements to localized constraints or “chokepoints” in the corridor where geometric and operational modifications are needed to improve traffic and safety operations. The major chokepoints are at Route 28, US 50, Route 123, and Route 243 (Nutley Street). The modifications include all the Express Lane new and modified access, Express Lane mainline entry and termination points in both directions, change of access to general purpose lanes at interchanges, and the elimination of existing access in Vienna area (Saintsbury Drive Loop Ramp). Note that currently no direct access is provided between Route 28 south of I-66 and I-66 west of Route 28, and that will continue to be the case in the Build Alternatives.

The list below summarizes the modified access locations for general purpose lanes, Express Lanes, and entry/exit points between general purpose lanes and Express Lanes. Detailed information on these modifications to the access points is given in the Appendix B.

General Purpose Lanes: − US 15 (modifications by others, under separate Interchange Modification Report) − Route 234 Business

− Route 28

− Fairfax County Parkway

− US 50

− Route 123 − Vaden Drive/Vienna Metrorail station

− Route 243 (Nutley Street)

− I-495 (general purpose lanes and Express Lanes)

Express Lanes: − New Crossing of I-66 west of US 15 (for Preferred Alternative only - 2040) − University Boulevard

− Route 234 Bypass (for Preferred Alternative) − Cushing Road park-and-ride lot (for Preferred Alternative - 2040) − Balls Ford Road park-and-ride lot − Route 28

− Stringfellow Road (east facing only)

− Fairfax County Parkway (from Eastbound Express Lanes)

− Monument Drive

− US 50 − Route 123

− Vaden Drive/Vienna Metrorail station

− I-495 (general purpose lanes and Express Lanes)

General Purpose and Express Lanes Transition via Slip Ramp or Flyover Ramp: − US 15 Entrance and Exit Ramps west of US 15 (Preferred Alternative - 2040)



− US 29 (Gainesville) Entrance and Exit Ramps between US 29 (Gainesville) and University Boulevard (Phase 1 only)

− Route 28 Slip Ramps / Flyover Ramps on both sides of Route 28 interchange

− Dunn Loring Flyover Ramp from general purpose lanes (between Route 243 (Nutley Street) and I-495)

As a result, operations on the I-66 general purpose lanes are expected to improve in Phase I and the Preferred Alternative as compared to No-Build conditions. The improved conditions and added capacity on the I-66 general purpose lanes will reduce the cut-through traffic on local networks and reduce the queuing impact from freeway ramps to adjacent intersections on surface streets.

The travel patterns in the existing conditions indicate that very little volume travels the entire corridor between US 15 and I-495 (less than 10 percent), with nearly 75 percent of traffic at the I-66/I-495 interchange being generated within Fairfax County. The most attractive origins and destinations for traffic from both ends of the corridor are Route 243 (Nutley Street), Route 123, US 50, Fairfax County Parkway and Route 28. This wide distribution of activity along the corridor supports a modification to the corridor at various interchange access points to accommodate future commuter travel patterns.

Finally, the majority of the existing transit service in the corridor is oriented to serve home-to-work travel in the morning and work-to-home travel in the evening. There is little-to-no contiguous mid-day transit service in the corridor and very little weekend transit service. All-day and weekend transit service that supports a greater number of origins and destinations will help reduce the number of single-occupancy vehicle (SOV) trips in the corridor. Additionally, travelers would benefit from receiving more information about the variety of travel choices available to them, including carpooling and vanpooling. These alternative travel choices will be enhanced with access to and from the I-66 Express Lanes and with more reliable travel times along the corridor.

3.1.2 Policy Point 2: Reasonable Alternatives The need being addressed by the request cannot be adequately satisfied by reasonable transportation system management (such as ramp metering, mass transit, and HOV facilities), geometric design, and alternative improvements to the Interstate without the proposed change(s) in access.

As stated in the Record of Decision (ROD) of the Tier 1 Environmental Impact Statement (EIS), approved by FHWA in November 2013, the transportation needs in this corridor cannot be met with a single stand-alone improvement concept; rather, a combination of improvements will be necessary, some of which can be implemented in the near term, while others can be realized over a longer term. The improvement concepts evaluated in the Tier 1 EIS include not only general purpose lanes and Express Lanes, spot locations and chokepoints, but also transit options.

Under the proposed Tier 2 Environmental Assessment, the I-66 corridor would be improved to provide:

At least three general purpose lanes in each direction. Two Express Lanes in each direction that would support:

− High-occupancy vehicle (HOV) users with three or more occupants.

− Low-occupancy (less than three occupants) toll-paying users (HOT).

− High-frequency bus service with predictable travel times. Direct access between the Express Lanes and new or expanded commuter lots.



In order to achieve the aforementioned improvements, 21 potential access-point locations were identified throughout the I-66 corridor. These access points include both general purpose lanes and Express Lanes. A unique aspect for the proposed project is to accommodate transit operations on Express Lanes to provide reliable mode choices to travelers. Therefore new access points to Express Lanes for transit operations are crucial to the success of the project. These access-point locations were compared against each other to determine which locations to carry forward in analysis and which to dismiss from further consideration. The 21 access-point location alternatives considered were:

US 15 US 15 Slip Ramps between US 15 and US 29 (Gainesville) US 29 (Gainesville) University Boulevard Route 234 Bypass Balls Ford Road park-and-ride lot Route 234 Business Slip Ramps between Route 234 Business and US 29 (Centreville) US 29 (Centreville) Route 28 Slip Ramps and Flyover Ramps between Route 28 and Stringfellow Road Stringfellow Road (east facing only) Fairfax County Parkway Monument Drive US 50 Slip Ramps between US 50 and Route 123 Route 123 Vaden Drive/Vienna Metrorail station Route 243 (Nutley Street) Dunn Loring Flyover Ramp (between Route 243 and I-495) I-495 (general purpose lanes and Express Lanes)

Travel demand model sensitivity testing was utilized to screen access-point locations throughout the I-66 corridor. The travel demand tests entailed running the Tier 2 Traffic and Revenue Model for the AM peak period for 2040 Build and the 2040 No-Build trip tables. If the access point demonstrated minimal demand, it was eliminated from further consideration. Geometric analysis also was conducted for access-point feasibility. Access location, type, and number of ramp lanes all were considered as part of the geometric analysis. If a fatal flaw was discovered, the access point was eliminated from further consideration.

Many combinations of alternatives were evaluated in both the Tier 1 and Tier 2 processes, and the multiple alternatives were screened and evaluated before being dismissed during the Tier 2 NEPA process, prior to arriving at the current Preferred Alternative.

As discussed in Chapter 8 and Chapter 9, the travel forecasting was performed using the regional travel demand model. The traffic operations analysis was conducted for the entire I-66 corridor including the adjacent interchanges of the crossroads and local roadway intersections. The study area thus covered sufficient area that allowed evaluation of all reasonable alternatives to cover the elements of this study. The evaluation included a baseline existing conditions assessment, a future intermediate year (2025) No-Build and Build conditions assessment, and a future design year (2040) No-Build and Build conditions assessment.



Transportation system management (TSM) strategies alone, such as ramp metering, mass transit, and improved striping and signing, will not solve the access issues identified in the Purpose and Need. The proposed project already incorporates a number of TSM components where they are feasible and appropriate. These components include ITS/Active Traffic Management (ATM), transit improvements, bicycle and pedestrian facility improvements, and travel demand management (TDM) solutions. In addition, the proposed project allows opportunities for future Metrorail extension along the corridor. From a design standpoint, the project development process for the proposed improvement plan considered a number of iterations and options for geometric design and access configurations. The following section gives examples of modified traffic signals, additional/modified turn lanes at intersections, auxiliary lanes for the freeway mainline, and improvements to park-and-ride lots along the corridor.

Modified traffic signals and turn lanes:

− Stringfellow Road and Express Lanes ramp intersection − Monument Drive and Express Lanes ramp intersection

− Route 234 Business and Balls Ford Road intersection

Auxiliary lanes: − I-66 general purpose lanes between Route 234 Bypass and US 29 (Gainesville) in both

directions − I-66 general purpose lanes between US 29 (Centreville) and Route 28 in both directions

− I-66 general purpose lanes between Route 28 and Fairfax County Parkway in both directions

− I-66 general purpose lanes between Fairfax County Parkway and US 50 in both directions

− I-66 general purpose lanes between US 50 and Route 123 in both directions − I-66 general purpose lanes between Route 123 and Route 243 in both directions

− I-66 general purpose lanes between Route 243 and I-495 in both directions

Park-and-ride lot improvements at existing facilities: − Cushing Road park-and-ride lot

− Monument Drive park-and-ride lot

3.1.3 Policy Point 3: Operational and Collision Analyses An operational and safety analysis has concluded that the proposed change in access does not have a significant adverse impact on the safety and operation of the Interstate facility (which includes mainline lanes, existing, new, or modified ramps, ramp intersections with crossroad) or on the local street network based on both the current and the planned future traffic projections. The analysis shall, particularly in urbanized areas, include at least the first adjacent existing or proposed interchange on either side of the proposed change in access. The crossroads and the local street network, to at least the first major intersection on either side of the proposed change in access, shall be included in this analysis to the extent necessary to fully evaluate the safety and operational impacts that the proposed change in access and other transportation improvements may have on the local street network. Requests for a proposed change in access must include a description and assessment of the impacts and ability of the proposed changes to safely and efficiently collect, distribute and accommodate traffic on the Interstate facility, ramps, intersection of ramps with crossroad, and local streets. Each request must also include a conceptual plan of the type and location of the signs proposed to support each design alternative.

The study area for operational analyses and safety performed as a part of this IJR satisfies the FHWA requirements for roadway network analysis. The traffic operational analyses and quantitative safety studies consistent with FHWA policy are documented in Chapters 9 and 10, respectively. Chapter 8 details the forecast traffic volumes for 2025 and 2040 and the methodology used to develop them.



The operational analysis and the safety analysis, performed as part of the change of access request, includes the general purpose lanes and Express Lanes mainline freeway segments, associated ramps and collector-distributor (C-D) roads for the length of the project, plus at least the first adjacent interchange on each side of the proposed Express Lanes termini. For the operational analysis in particular, the I-66 corridor to the east of the I-495 interchange included the interchange with the Dulles Toll Road, and the influence area for I-495 extended to the Route 7 interchange to the north and the Gallows Road interchange to the south. At Route 28, Fairfax County Parkway, and US 50, the next adjacent interchanges on either side of I-66 were also included in the analysis. At each of the interchanges being studied, the crossroads included the ramp terminal intersections and adjacent local street intersections. On some crossroads, multiple adjacent intersections were considered part of the influence area of the interchange and as such were included in the operational analysis given the impact to the local network.

The proposed plan for I-66 will result in marked operational improvements to the overall system by increasing capacity and improving access on the general purpose lanes by transferring some of the traffic currently using the over-saturated general purpose lanes to the proposed Express Lanes. The Express Lanes, which provide much more capacity than the current peak directional HOV lane that is not physically separated from the general purpose lanes, operate at desirable travel speeds. In addition, adjacent crossroad intersections to the interchanges and local network also benefit from the proposed plan as indicated by less queue spillback from the I-66 mainline and less cut-through traffic within the influence area as a result of oversaturated conditions under the No-Build scenarios. A detailed assessment of traffic operations using microsimulation (VISSIM) is presented in Chapter 9 of this document.

From a safety perspective, detailed qualitative and quantitative safety analyses were conducted for the corridor on the general purpose lanes, ramps, arterials, and intersections and are detailed in Chapter 10. Highway safety and design professionals used the Highway Safety Manual (HSM) as a resource to inform project development, design, and decision making in determining design features with the greatest potential to benefit safety. The crash prediction methods identified in the HSM use key elements for roadway design and traffic data that are fundamental to project development. Two safety analysis tools were used to evaluate the various components of the network: ISATe for freeway analyses and Extended HSM Spreadsheets for the arterial and intersections analyses. The ramps were evaluated and compared using a qualitative method through the computation of equivalent property damage only (EPDO) crashes.

Planning level crash analysis was performed using industry standard practice and highway safety analysis tools. This analysis evaluated the safety performance of existing conditions and assessed the differences between the 2040 No-Build and Build alternatives within safety zones. These zones correspond to interchanges, freeway segments, ramp segments, intersections, and arterials affected by new ramps or access to/from the Express Lanes facility. Both qualitative and quantitative analyses were conducted to evaluate existing, No-Build, and Preferred Alternative conditions along the I-66 corridor. The safety analyses focused on the network as a system, including mainline segments, ramps, C-D roads, intersections, and arterials.

The results of the safety analysis showed that the highest crash frequencies (both existing and predicted) in the study area occurred in the vicinity of the entrance and exit ramps at interchanges along the I-66 mainline. Additionally, the magnitude of crashes was higher in the eastern portion of the corridor between the US 29 (Centreville) interchange and the I-495/I-66 interchange. The calculated crash rates, mainline histograms, and ISATe existing conditions analyses support this conclusion. The higher crash frequencies, both existing and predicted, in the eastern portion of the corridor were attributed primarily to



the higher levels of traffic congestion and geometric restrictions. More detailed information is provided in Chapter 10 – Crash and Safety Assessment.

The quantitative ISATe safety evaluation of the mainline I-66 operations revealed an overall improvement in safety in 2040 under the Preferred Alternative compared to the No-Build. The most critical safety locations will continue to be the areas with the highest traffic volume exposure between Fairfax County Parkway and I-495. The detailed results of these analysis are described in Chapter 10 of this IJR.

Supporting documentation also includes a functional signing plan and assumptions used in developing a signing concept, as provided in Chapter 13 of this document.

3.1.4 Policy Point 4: Access Connections and Design The proposed access connects to a public road only and will provide for all traffic movements. Less than “full interchanges'' may be considered on a case-by-case basis for applications requiring special access for managed lanes (e.g., transit, HOVs, HOT Lanes) or park-and-ride lots. The proposed access will be designed to meet or exceed current standards.

The proposed plan provides access to public roads for all the interchange improvements. A few partial interchanges were proposed or retained and incorporated into the access configuration to connect to the I-66 Express Lanes in the Preferred Alternative concept and Phase I concept because of special access conditions associated with Express Lanes, transit service, and park-and-ride lot connections. One exception is the proposed partial interchange concept of Route 28 and Braddock Road north of I-66, which does not allow access to or from the north by way of Braddock Road. The intention for the partial interchange is to limit impacts to Fairfax County’s E.C. Lawrence Park, as required by the National Environmental Policy Act (NEPA). Traffic destined to the north will still be able to use Walney Rd to access the next interchange north on Route 28 (Westfields Boulevard).

The following partial interchanges are provided in the Preferred Alternative concept and/or Phase I concept due to special access conditions associated with the Express Lanes, transit service, and park-and-ride lot connections:

Route 234 Bypass Express Lanes access to and from the west only (Preferred Alternative only) – access from I-66 Express Lanes eastbound to Route 234 southbound and from Route 234 northbound to I-66 Express Lanes westbound. This access would be paired with the access at Cushing Road described below.

Route 234 Bypass Express Lanes access to and from the east only, via Cushing Road park-and-ride lot (Preferred Alternative only) – access from I-66 Express Lanes westbound to park-and-ride lot and from park-and-ride lot to I-66 Express Lanes eastbound.

Balls Ford Road Express Lanes access to and from the east only, via park-and-ride lot – access from I-66 Express Lanes westbound to park-and-ride lot and from park-and-ride lot to I-66 Express Lanes eastbound.

Route 28 interchange: - Access is not provided from I-66 eastbound to Route 28 southbound or from I-66 Express

Lanes eastbound to Route 28 southbound (consistent with access today, which is provided at adjacent US 29 interchange).

- Access is not provided from Route 28 northbound to I-66 westbound or I-66 Express Lanes westbound (consistent with access today, which is provided at adjacent US 29 interchange).

- Direct access is not provide from I-66 Express Lanes westbound to Route 28 southbound; however, travelers along I-66 Express Lanes westbound can use an upstream flyover ramp



to access to the I-66 general purpose westbound lanes and the ramp to Route 28 southbound.

- Access is not provided from Braddock Road to Route 28 northbound or from Route 28 southbound to Braddock Road.

- New east-facing and west-facing Express Lane access at: Northbound Route 28 to eastbound Express Lanes Southbound Route 28 to eastbound Express Lanes Southbound Route 28 to westbound Express Lanes Eastbound Express Lanes to northbound Route 28 Westbound Express Lanes to northbound Route 28

Stringfellow Road Express Lanes access to and from the east only – access from I-66 Express

Lanes westbound to Stringfellow Road and from Stringfellow Road to I-66 Express Lanes eastbound.

US 50 Express Lanes access – in addition to all movements for I-66 general-purpose traffic to and from US 50, access is provided from US 50 eastbound to I-66 Express Lanes eastbound and from I-66 Express Lanes westbound to US 50 westbound.

Route 123 Express Lanes access to and from the east only – in addition to all movements for I-66 general-purpose traffic to and from Route 123, access is provided via a signalized intersection from Route 123 to I-66 Express Lanes eastbound and from I-66 Express Lanes westbound to Route 123.

Vaden Drive Express Lanes access to and from the west only – access from I-66 Express Lanes eastbound to Vaden Drive and from Vaden Drive to I-66 Express Lanes westbound, providing Express Lanes access to and from the Vienna Metrorail station.

I-495 interchange: - Direct access from I-66 general purpose lanes eastbound is not provided to I-495 Express

Lanes northbound or southbound; however, indirect access is provided via an upstream flyover ramp from I-66 general purpose lanes eastbound to I-66 Express Lanes eastbound.

- Access is not provided from I-66 Express Lanes eastbound to I-495 general purpose lanes northbound.

- Access is not provided from I-66 general purpose lanes westbound to I-495 northbound (general purpose or Express Lanes), consistent with the interchange as it exists today.

- Access is not provided from I-495 general purpose lanes southbound to I-66 Express Lanes westbound.

- Access is not provided from I-495 southbound (general purpose or Express Lanes) to I-66 eastbound, consistent with the interchange as it exists today.

The ramp access was determined based on 25 different model runs for various access combinations. These partial interchanges do not violate policy because they provide alternative access to the I-66 corridor for the modes listed in the policy point: transit, HOV, and HOT.

The design of the proposed I-66 Express Lanes and adjacent service interchanges is intended to meet or exceed American Association of State Highway and Transportation Officials (AASHTO) design standards, where feasible. However, it is acknowledged that there will be exceptions to standards to better meet the needs of the project and to minimize impacts to adjacent properties. These exceptions to standards generally stem from substandard existing conditions that cannot be corrected within the stated purpose and need of the project and in areas where FHWA or the USACE expressed concerns with impacts or there were Section 4(f) resources. These exceptions to standards are identified in Chapter 7 of this



document and further documented in detail in the Exceptions to Standards Report to be submitted for review by VDOT and FHWA.

Even though 2021 is the anticipated opening year for the project, the year 2025 was used as the interim year to account for the time it takes for traffic demand to reach equilibrium, which is estimated to be approximately three years. The design year was chosen to be 2040 as was agreed upon by VDOT and FHWA in the Scoping Framework document.

3.1.5 Policy Point 5: Land Use and Transportation Plans The proposal considers and is consistent with local and regional land use and transportation plans. Prior to receiving final approval, all requests for new or revised access must be included in an adopted Metropolitan Transportation Plan, in the adopted Statewide or Metropolitan Transportation Improvement Program (STIP or TIP), and the Congestion Management Process within transportation management areas, as appropriate, and as specified in 23 CFR part 450, and the transportation conformity requirements of 40 CFR parts 51 and 93.

The proposed project is the culmination of many years of transportation plans for the area. The proposed improvements to I-66 are consistent with local and regional land use plans, including the Fairfax County and Prince William County Comprehensive Plans. The improvements are also consistent with the Constrained Long-Range Transportation Plan (CLRP) that pertains to the study area and is adopted by the Metropolitan Washington Council of Governments (MWCOG) -- the metropolitan planning organization (MPO) for the Washington Metropolitan area. The entire corridor of the project is included in the National Capital Region Transportation Planning Board’s approved FY 2011-2016 Transportation Improvement Program (TIP) and 2015 CLRP (approved on October 21, 2015), which were found to conform to the State Implementation Plan. The Virginia Commonwealth Transportation Board (CTB) selected and approved the Preferred Alternative included in this IJR on October 27, 2015. The most recent project scope update that includes minor technical revisions (as presented in this IJR and the NEPA documentation) has been incorporated into the updated conformity determinations for MWCOG, with FHWA approval expected by the end of year (December 2016 at the latest). The proposed project involved extensive coordination with MWCOG, Fairfax County, Prince William County, and other local agencies.

3.1.6 Policy Point 6: Future Interchanges In corridors where the potential exists for future multiple interchange additions, a comprehensive corridor or network study must accompany all requests for new or revised access with recommendations that address all of the proposed and desired access changes within the context of a longer-range system or network plan.

The Preferred Alternative identified in the EA and selected in the FONSI includes a program of multimodal improvements between Haymarket and I-495. A subset of the Preferred Alternative was developed and identified in the I-66 Interchange Justification Report (IJR) as Phase 1, which provides for a phased approach to delivering the Preferred Alternative, and includes Express Lanes for 22 of the Project’s 25 miles, from University Boulevard in Gainesville to I-495. VDOT is procuring a private Developer through the Virginia Office of Public Private Partnerships (VAP3) to design, build, own, and operate the Express Lanes, and to implement Phase 1. The traffic analysis included in the IJR for the design year 2040 is based on the Preferred Alternative as noted in the EA. VDOT is committed to implement the remaining elements of the Preferred Alternative by the year 2040, to the extent additional travel demand in the corridor warrants, and will seek additional funding to implement needed



improvements in conjunction with regional and state funding plans. This includes additional access points and interchanges identified in the Preferred Alternative as being constructed sometime after Phase 1 is completed.

The proposed improvements to I-66 and other projects that entail adjacent or nearby future interchange improvements are included and adopted in the CLRP for the Washington Metropolitan region. The CLRP looks comprehensively at the transportation needs and improvements throughout the Capital region. The proposed new and revised access points were assessed by network-wide traffic analyses that focused on not only I-66, but also Route 28, I-495, and the adjacent intersections to these freeway corridors, including improvements identified in the CLRP and local plans The traffic analyses cover not only the study area but the area of influence, which can be seen in Exhibit 4.1 and Exhibit 4.2 in the IJR. The traffic analyses considered all other interchanges planned in the future within the area of influence. The operational analyses conducted for this IJR considered all of the elements in the CLRP that affect the project corridor, including the planned conversion of HOV lanes to Express Lanes for I-66 between I-495 and US 29 in Rosslyn and the addition of HOV lanes to other regionally significant routes, such as Route 28 and Fairfax County Parkway. All new and revised access points are supported by these comprehensive network study recommendations. The project analysis included traffic and impacts from future access improvements, external to the I-66 project and implemented by others, such as the Bi-County Parkway and associated new interchange ramps at the I-66/Route 234 Bypass interchange.

3.1.7 Policy Point 7: Coordination When a new or revised access point is due to a new, expanded, or substantial change in current or planned future development or land use, requests must demonstrate appropriate coordination has occurred between the development and any proposed transportation system improvements. The request must describe the commitments agreed upon to assure adequate collection and dispersion of the traffic resulting from the development with the adjoining local street network and Interstate access point.

The proposed new and revised access points in this project are not associated with any specific private development plans. The proposed access points will not be used to provide access between any new or expanded development and the interstate facility. These proposed improvements are envisioned to address existing traffic congestion and safety issues and to better facilitate traffic flow and operations for the future design year. The improvements are needed to provide access to the Express Lanes, which are connected to existing and expanded park-and-ride lots and adjacent service interchanges. However, the location of the direct ramps serving the Express Lanes were carefully vetted and coordinated with the local jurisdictions in order to identify the optimal locations for access and corresponding park-and-ride lots/express bus stations, based on density of proposed surrounding land use, as well as future activity centers that were focused around transit-oriented development. Local street networks were evaluated and potential improvements were identified to ensure that they would accommodate the proposed new and expanded existing park-and-ride lots.

The park-and-ride locations were originally identified in the 2009 I-66 Transit/TDM Study. The 2009 study identified general locations for park-and-ride lots, specific potential parcels, and potential size based on a demand analysis using parking lot utilization data, license plate survey data, and drive access to transit and high-occupancy vehicle (HOV) demand forecasts. Specific locations were identified and evaluated at a high level based on factors such as effect on adjacent roadways, construction and maintenance of traffic costs, right-of-way, and access considerations.

In the current Tier 2 efforts, the 2009 analysis was updated and the locations were refined. The demand was reassessed with new data and, using comparisons with existing park-and-ride lots in the region, new



sizes for the lots were developed. Input was gained from the Transit Technical Advisory Group (TTAG) which consists of local jurisdictions, transit agencies, and other project stakeholders. TTAG members were involved in confirming these locations, discussing access locations, and working with land owners when applicable. Final design for the park-and-ride facilities would also be subject to local and VDOT/DRPT approval.

Detailed environmental analysis was completed and conceptual layouts were developed to determine the space needed and potential configuration of the proposed lots. During the demand analysis, two years were used to assess the number of spaces – 2025 and 2040. In the draft Project Technical Requirements, it is required that the project park-and-ride facilities should be constructed by opening year to meet the 2025 demand and be expanded before 2040 to meet the 2040 demand. The land acquisition and the capital costs associated with the construction of the park-and-ride lots would be the responsibility of the Developer. By 2025 there will be a minimum of approximately 4,300 spaces in the four project park-and-ride lots. By 2040, there will be 5,900 total spaces in four expanded facilities.

3.1.8 Policy Point 8: Environmental Processes The proposal can be expected to be included as an alternative in the required environmental evaluation, review and processing. The proposal should include supporting information and current status of the environmental processing.

The Tier 2 Final Environmental Assessment (Tier 2 EA) for the proposed I-66 Corridor Improvements Project from US 15 in Prince William County to I-495 in Fairfax County has been prepared in accordance with requirements of NEPA through a joint effort by FHWA, VDOT, and DRPT. The Federal Transit Administration, the US Army Corps of Engineers, and the US Environmental Protection Agency have served as cooperating agencies. This Tier 2 study was undertaken to advance improvements identified at a conceptual level in the Tier 1 EIS and Tier 1 ROD published in November 2013.

The first draft of the Tier 2 EA was available for public review and comment in May and June 2015. In addition to being posted on the project website, the Draft EA and supporting technical reports were available for review at the four public hearings that were held in May and June 2015 at locations along the project corridor. All comments received on the Draft EA have been considered and substantive comments were addressed in a Revised EA that included identification of the Preferred Alternative, published in January 2016. The Final EA, which accounted for final comments on the Preferred Alternative and included revisions to the Preferred Alternative as shown in the RFP Conceptual Plans in Appendix B of this IJR, was approved on June 21, 2016. A FONSI was issued by FHWA on June 22, 2016, in parallel with a complementary Final IJR submission.


I-66 Corridor Improvements 4-1

CHAPTER 4. STUDY AREA

4.1 Overview The study area covered a 25-mile section of I-66 between US 15 in Prince William County and I-495 in Fairfax County. The analysis area included I-66, its parallel arterial routes US 50 and US 29, and several key routes serving north-south travel including US 15, Route 234, Fairfax County Parkway, Route 123, and I-495. In addition, Route 28 between the Westfields Boulevard interchange to the north and the interchange at US 29 (Centreville) to the south was added to the study area. The general location for studying future highway and transit improvements in Tier 2 is within the existing I-66 corridor as defined in the Tier 1 Draft EIS, with the exception of Virginia Railway Express (VRE) improvements for which the general location is the existing VRE alignment.

4.2 Project Location Map Exhibit 4.1 and Exhibit 4.2 shows the various components of the project study area for the I-66 Tier 2 study:

Blue – Adjacent Projects.

Green – IJR study area. The IJR study area includes the I-66 corridor between Old Tavern Road and I-495, inclusive of all ramp termini.

Yellow – IJR area of influence. The IJR area of influence, which is inclusive of the traffic analysis model extents, will be fully analyzed to the same extent as the IJR study area and generally extends one intersection or interchange beyond the IJR study area:

I-66 interchanges with Old Tavern Road, Route 7, and Dulles Toll Road I-495 interchanges with Route 7 and US 50

- Study area is between Route 7, US 29, US 50, and Route 650 (Gallows Road) Other major intersections or interchanges

- Route 28 and US 29 - Fairfax County Parkway and US 29/West Ox Road (Route 608) and Fair Lakes

Parkway/Monument Drive - Fairfax County Parkway and US 29 - West Ox Road and US 50

Generally, one or two major intersections adjacent to I-66 ramps.

Tier 2 NEPA study area. The project’s Area of Potential Effect (APE) is included in the concurrent Tier 2 Final EA, which is being completed in coordination with this IJR and preliminary engineering efforts.

4.3 Logical Termini FHWA regulations implementing NEPA require that:

“In order to ensure meaningful evaluation of alternatives and to avoid commitments to transportation improvements before they are fully evaluated, the action evaluated in each Environmental Impact Statement (EIS) or Finding Of No Significant Impact (FONSI) shall:



1. Connect logical termini and be of sufficient length to address environmental matters on a broad scope;

2. Have independent utility or independent significance, i.e., be usable and be a reasonable expenditure even if no additional transportation improvements in the area are made; and

3. Not restrict consideration of alternatives for other reasonably foreseeable transportation improvements.”

The central basis of all three of the above criteria is that projects have rational end points, that is, end points that are based on valid and sound reasoning. Among the factors considered in establishing the termini for this project are the following:

The western terminus of the area of influence was identified as Old Tavern Road in the Plains because it represents a rural interchange east of which the area transitions from rural to suburban over a corridor length of 9 miles. Minimal population and employment growth is expected in the vicinity of this interchange. It was considered as part of the area of influence to serve as a network filter for traffic entering and exiting the network as it is not identified for any near- or long-term transportation network improvements. The next substantial urbanized area is the Town of Haymarket and surrounding Prince William County, located 9 miles to the east at the US 15 interchange.

I-66 connects to I-495, which is comprised of general purpose and Express Lanes. Connection to the Express Lanes will expand the regional reach and continuity of the Express Lanes system along I-495, I-95, and the proposed Express Lanes on I-66. However, the easternmost terminus of the area of influence (Dulles Toll Road) was identified as the point at which the freeway is reduced to the current four-lane configuration of I-66 inside I-495. It is also the last decision point for roadway users to choose an alternate limited-access facility that provides access to points west of I-495.

The proposed project can stand alone without requiring other improvements on adjoining sections of I-495 and the Dulles Toll Road. As part of the project, improvements have been identified for the Route 28 corridor between US 29 (Centreville) and Westfields Boulevard. This was previously being considered as a separate, standalone project. However, with the study of the larger I-66 Corridor Improvements Project, these improvements have been absorbed into the project and are considered to be part of the proposed improvements. The transition to the Express Lanes and general purpose lanes systems at I-495 has been designed such that additional improvements will not be required north or south of the transition area as a result of the project to specifically mitigate project-related impacts. A project with separate purpose and need, the study of Express Lane operations east of I-495 along I-66 (Inside the Beltway project), has been identified by VDOT. This project will also reduce downstream congestion beyond the eastern terminus, thus improving operations at the eastern terminus interface with the Express Lanes and general purpose lanes.

The proposed project does not constrain the consideration of alternatives for other reasonably foreseeable alternatives beyond the project limits.

The 25-mile length of the study area corridor extends across Fairfax County, Prince William County, the Town of Haymarket, the northern edge of the City of Fairfax, the southern edge of the Town of Vienna, and the southern edge of the City of Falls Church, and provides ample length to address transportation and environmental matters on a broad scale. Moreover, the extent of the project’s environmental impacts is contained mostly within the existing footprint of the highway corridor, with little if any extension beyond the proposed limits of the project.



4.4 Study Area Boundaries and Facilities Included As noted above, the study area boundaries included a 25-mile section of I-66 between US 15 and I-495, along with the parallel arterial routes and several key routes serving north-south travel. The area of influence extends beyond these limits and includes one interchange to the east and west along I-66 at Route 7 and Old Tavern Road, respectively. In addition, four interchanges were included along I-495 as part of the area of influence: Route 7, US 29, US 50, and Gallows Road.

The core communities in the vicinity of the study area are Prince William County and Fairfax County, the Town of Haymarket, the City of Fairfax, the Town of Vienna, and the City of Falls Church. These communities will be impacted to varying degrees as part of this study. The interchanging roadways included in the study area and the intersections along these crossroads that have been analyzed are listed below.

US 15 Heathcote Boulevard I-66 WB On/Off-Ramps I-66 EB On/Off-Ramps John Marshall Highway/Washington Street

US 29 (Gainesville) Heathcote Boulevard and Heritage Hunt Drive (not located on US 29) University Boulevard Heathcote Boulevard Linton Hall Road

Route 234 Bypass Balls Ford Road Cushing Road (not located on Route 234)

Route 234 Business Battleview Parkway I-66 WB On-Ramp I-66 EB On/Off-Ramps Automotive Drive Balls Ford Road

US 29 (Centreville) Trinity Parkway I-66 EB On/Off-Ramps I-66 WB On/Off-Ramps O’Day Drive Park-and-Ride Lot Driveway Stone Road

Route 28 Ellanor C. Lawrence Park Braddock Road/Walney Road I-66 WB Off-Ramp I-66 EB On-Ramp

Stringfellow Road (HOV Access) Fair Lakes Boulevard Park-and-Ride Lot Driveway I-66 HOV Access Ramp Westbrook Drive Centreville Farms Road

Monument Drive (HOV Access) West Ox Road Fair Lakes Parkway Fair Lakes Promenade Drive I-66 HOV Access Ramp Government Center Parkway Monument Corner Drive

US 50 Fair Oaks Mall Right-In/Right-Out (2) Waples Mill Road Jermantown Road

Route 123 Jermantown Road/Blake Lane Rose Forest Drive/White Granite Drive Oak Place/Eaton Place US 29/US 50

Vaden Drive I-66 WB Off-Ramp to Country Creek Road I-66 EB On-Ramp from Saintsbury Drive



Route 243 (Nutley Street) Virginia Center Boulevard/Marshall Road SW Saintsbury Drive/Swanee Lane Hermosa Drive US 29 In addition to the interchanges along I-66 within the project study area, additional arterial interchanges were considered along with adjacent interchanges along I-495. These intersections and interchanges in the expanded study area as well as in the area of influence included those listed below.

University Boulevard Wellington Road

Westfields Boulevard at Route 28 Park Meadow Drive Newbrook Drive Stonecroft Boulevard

Monument Drive/Fair Lakes Parkway at Fairfax County Parkway Monument Drive at SB Off-Ramp Monument Drive at NB On-Ramp Fair Lakes Parkway at SB On-Ramp Fair Lakes Parkway at NB Off-Ramp

US 29 at Fairfax County Parkway Gunpowder Rd/US 29 SB On-Ramp Gunpowder Rd/US 29 NB Off-Ramp SB Off-Ramp/US 29 SB Service Road SB On-Ramp/US 29 NB Service Road NB On-Ramp/US 29 SB Service Road NB Off-Ramp/US 29 NB Service Road West Ox Road/US 29 SB Off-Ramp West Ox Road/US 29 NB On-Ramp

West Ox Road at US 50 US 50 EB Off-Ramp Legato Road

I-495 Route 7 US 29 US 50 Gallows Road

Route 7 Idylwood Road/Reddfield Drive I-66 EB Off-Ramp Dale Drive/Falls Church Drive George Mason High School Driveway Chestnut Street Shreve Road/Haycock Road I-495 NB On/Off-Ramps I-495 SB On/Off-Ramps I-495 Express Lane On/Off-Ramps US 29 at I-495 I-495 Express Lane On/Off-Ramps US 50 at I-495 I-495 NB On/Off-Ramps I-495 SB On/Off-Ramps Gallows Road at I-495 Woodburn Road/I-495 SB Off-Ramp/Gallows Road I-495 NB On/Off-Ramps I-495 SB On-Ramp I-495 Express Lane On/Off-Ramps Old Tavern Road Main Street I-66 WB On/Off-Ramps I-66 EB On/Off-Ramps Harrison Road Dulles Toll Road at I-66 I-66 WB Off-Ramp I-66 EB On-Ramp



CHAPTER 5 EXISTING CONDITIONS

5.1 Demographics I-66 serves as a major commuting route connecting Washington, DC, and other major activity centers within suburban Northern Virginia. A major interchange in the eastern portion of the I-66 corridor provides connections to I-495, which connects major activity centers all around Washington, DC. The interchange also provides access to and from the I-495 Express Lanes, which are indirectly integrated with the Express Lanes on I-95. In addition, I-66 serves as a major route for east-west travel across the northern part of Virginia, connecting the Washington metropolitan area to I-81 near Winchester, VA.

Local communities directly adjacent to the corridor that are expected to be served by the proposed improvements to I-66 are listed in Table 5.1. 2010 and 2014 population data was obtained from the US Census Bureau. Where 2014 data was unavailable, data was obtained from the American Community Survey (ACS) as noted in Table 5.1 with an asterisk.

Table 5.1: Communities Served by the Proposed Project

Community County Population (2010) Population (2014)

Idylwood Fairfax 17,288 17,643* Dunn Loring Fairfax 8,803 9,360*

Merrifield Fairfax 15,212 15,873* Town of Vienna Fairfax 15,687 16,459

Oakton Fairfax 34,166 36,860* City of Fairfax Fairfax 22,565 24,483

Fair Oaks Fairfax 30,223 32,392* Fair Lakes Fairfax 7,942 7,368* Centreville Fairfax 71,135 73,677*

Sudley Prince William 16,203 16,221* Bull Run Prince William 14,983 14,570*

Linton Hall Prince William 35,725 39,944* Gainesville Prince William 11,481 12,145*

Source: US Census Bureau, 2010, 2014; *2014 population estimate provided by the American Community Survey (ACS)

Fairfax County is the most populated county in the Commonwealth of Virginia and the metropolitan Washington, DC, area. In addition, it is the largest suburban office market in the metropolitan Washington, DC, area, and the second largest in the nation, with more than 115.8 million square feet of office space. Prince William County is characterized by suburban and rural residential areas and is growing at above-average rates compared to the rest of the Commonwealth. Economic conditions within Prince William County promote residential development and job growth due to the lower gas prices and interest rates, improving job market, and affordable housing compared to neighboring counties.

5.2 Land Use The parcels adjacent to the I-66 corridor are mostly built out. Adjacent land use is a mix of residential, industrial, office, and commercial and is typical of suburban development in close proximity to a major metropolitan city. At the interchange with I-495, an industrial park is seeing transit-oriented development convert previous warehouse and industrial land uses to mixed-use commercial, office, and residential



spaces. Fairfax Center Area is host to a number of suburban business parks and the regional Fair Oaks Mall. This area has evolved due to the convenient access to I-66 and the interregional thoroughfares of US 50, US 29, and Fairfax County Parkway. The Dulles International Airport, located to the north of I-66 by way of Route 28, draws local and regional traffic to the area as one of the major airports in the Washington metropolitan area. In the western portions of the study area, a mix of industrial and commercial land uses border I-66 and are provided access by way of Route 234 Business, Route 234 Bypass, and US 29 (Gainesville).

In addition to the built-out areas, there are a number of parks adjacent to the corridor. The publicly owned Conway Robinson Memorial State Forest (Department of Forestry), Manassas National Battlefield Park (National Park Service), Bull Run Regional Park (Northern Virginia Regional Park Authority), Cub Run Stream Valley Park (Fairfax County), Centre Ridge North Park (Fairfax County), Ellanor C. Lawrence Park (Fairfax County), Random Hills Park (Fairfax County), Providence Elementary School baseball fields (Fairfax County), East Blake Lane Park (Fairfax County), Southside Park (Town of Vienna), George C. Yeonas Park (Vienna Little League), and Dunn Loring Park (Fairfax County) are all adjacent to the I-66 right-of-way. Other than potential noise impacts at the Providence Elementary School baseball fields, these parks or recreation areas would not be impacted.

5.3 Existing Road Geometry and Access Locations The interstate and local roadway network in the project area consists of major roadways that carry significant amounts of vehicular traffic on a daily basis throughout the I-66 corridor. The geometric configurations of these roadways are illustrated in Exhibit 5.1. The roadways are discussed in greater detail in the following sections.

5.3.1 I-66 Corridor I-66 is classified as an urban interstate by FHWA and serves as a major east-west corridor that provides direct access to Washington, DC. The stretch of interstate evaluated as part of this study travels through the counties of Prince William and Fairfax in the Commonwealth of Virginia. In addition, the easternmost portion of I-66 in Fauquier County was considered to be within the area of influence for this study. Below is a progressive description of the I-66 corridor from west to east, identified by mile markers (MM). Exhibit 5.1 provides an overview of the I-66 corridor, including the number of lanes, median treatment, shoulder lanes, and posted speed limit, as well as the configuration of the intersecting roadways.

MM 31 – MM 39: I-66 is a four-lane divided highway (combination of grass and barrier-separated median) from Old Tavern Road to approximately 1 mile west of US 15. There are no high-occupancy vehicle (HOV) lanes on this segment of I-66, and the speed limit is 70 mph. Within this segment, access is provided to Old Tavern Road.

MM 39 – MM 42: I-66 is a four-lane divided highway (grass median) from approximately 1 mile west of US 15 to Catharpin Road, an overpass west of US 29 (Gainesville). There are no HOV lanes on this segment of I-66, and the speed limit is 65 mph. Within this segment, access is provided to US 15.

MM 42 – MM 44: I-66 transitions from a four-lane divided highway to an eight-lane divided highway (grass median) between Catharpin Road and University Boulevard, an overpass east of US 29 (Gainesville). Westbound HOV lanes terminate at the US 29 overpass (MM 43), at which point the general purpose lanes transition to a four-lane cross section in the direction of US 15. Within this segment, access is provided to US 29 (Gainesville) and to Heathcote Boulevard north of I-66.



MM 44 – MM 47: I-66 is an eight-lane divided highway (grass median) from University Boulevard to Route 234 Business. A single inside HOV lane and three general purpose lanes are provided in each direction. The speed limit is 65 mph west of MM 47. The speed limit is reduced to 60 mph at MM 47, the Route 234 Business interchange. Within this segment, access is provided to Route 234 Bypass and Route 234 Business. Access is also provided to/from the Manassas Welcome Center/Rest Area at MM 48.

MM 47 – MM 52: I-66 is an eight-lane divided highway (barrier-separated median) from Route 234 Business to US 29 (Centreville). A single inside HOV lane and three general purpose lanes are provided in each direction. The speed limit is 60 mph west of MM 51.5. The speed limit is reduced to 55 mph at MM 51.5, approximately 0.5 miles west of the US 29 interchange (Centreville). Within this segment, access is provided to US 29 (Centreville).

MM 52 – MM 58: I-66 is an eight-lane divided highway (combination of grass and barrier-separated median) from US 29 (Centreville) to US 50. A single inside HOV lane and three general purpose lanes are provided in each direction, and the speed limit is 55 mph. Within this segment, access is provided to Route 28, Stringfellow Road (HOV-only directional access ramp), Fairfax County Parkway, Monument Drive (HOV-only directional access ramp), and US 50.

MM 58 – MM 62: I-66 is a six-lane divided highway (combination of grass and barrier-separated median) from US 50 to Vaden Drive. A single inside HOV lane and two general purpose lanes are provided in each direction, and the speed limit is 55 mph. The outside shoulders function as general purpose travel lanes in the peak direction of travel. The eastbound shoulder lane is open to all traffic weekdays between 5:30 a.m. and 11:00 a.m., and in the westbound direction, between 2:00 p.m. and 8:00 p.m. Within this segment, access is provided to Route 123 and Vaden Drive.

MM 62 – MM 64: I-66 is a six-lane divided highway (Metrorail Orange Line inside median) from Vaden Drive to approximately 1 mile west of I-495. A single inside HOV lane and two general purpose lanes are provided in each direction, and the speed limit is 55 mph. The outside shoulders function as general purpose travel lanes in the peak direction of travel. The eastbound shoulder lane is open to all traffic weekdays between 5:30 a.m. and 11:00 a.m., and in the westbound direction, between 2:00 p.m. and 8:00 p.m. Within this segment, access is provided to Route 243.

MM 64 – MM 67: I-66 transitions from an eight-lane divided highway (Metrorail Orange Line inside median) to a four-lane divided highway at the interchange with I-495. West of I-495, a single inside HOV lane and three general purpose lanes are provided in each direction, and the speed limit is 55 mph. In the eastbound direction, the outside lane functions as an auxiliary lane that becomes an exit onto I-495 southbound. East of I-495, I-66 operates as an HOV-only facility in the peak direction of travel. Within this segment, access is provided to I-495 and Route 7.

5.3.2 Interchanges and Intersecting Roadways Within the project’s area of influence, there are 13 grade-separated interchanges that provide direct access to I-66, some of which are restricted to HOV use only during peak travel periods. Three additional interchanges are considered to be within the area of influence of the project study area (Old Tavern Road, Route 7, and the Dulles Toll Road). The following are brief descriptions of the roadways that connect with I-66, presented from west to east. Exhibit 5.1 provides an overview of the I-66 corridor interchanges and provides an overview of the intersecting roadways.

Old Tavern Road: Old Tavern Road is oriented in a north-south direction and is a four-lane divided

roadway classified as a rural major collector. Its interchange with I-66 is approximately 9 miles west of US 15. The posted speed limit along Old Tavern Road is 55 mph at its interchange with I-66.



US 15: US 15 is oriented in a north-south direction and is a four-lane divided roadway classified as an

urban minor arterial. The posted speed limit along US 15 is 40 mph at its interchange with I-66. US 15 is a primary connecting roadway between Route 7 to the north and US 29 to the south.

US 29 (Gainesville): US 29 is designated as a north-south route, but in the vicinity of I-66 in

Gainesville, the roadway is oriented in a northeast-southwest direction. Construction of a grade-separated interchange at its intersection with Linton Hall Road, located less than 1 mile to the south of I-66, was completed in the summer of 2015. US 29 is classified as an urban principal arterial south of I-66 and an urban minor arterial north of I-66. In October 2014, US 29 was configured as a four-lane divided roadway with a posted speed limit of 45 mph south of its interchange with I-66 and 55 mph to the north. This geometry is what is reflected in the existing conditions model.

University Boulevard: University Boulevard is oriented in a north-south direction and is a four-lane

divided roadway classified as an urban collector. University Boulevard passes over I-66 approximately 0.75 miles east of the US 29 (Gainesville) interchange and provides a connection between US 29 and Wellington Road. It has a posted speed limit of 45 mph.

Route 234 Bypass: Route 234 Bypass is oriented in a north-south direction and terminates at its

interchange with I-66. It is a four-lane divided roadway classified as an urban principal arterial. The posted speed limit is 45 mph in the northbound direction approaching the interchange with I-66 and is 55 mph to the south. Route 234 serves as a critical link through Prince William County, connecting I-66 to the north with I-95 and US 1 to the south.

Route 234 Business: Route 234 Business is oriented in a north-south direction and is classified as

an urban minor arterial. It is a four-lane divided roadway north of I-66 and a six-lane divided roadway to the south. The posted speed limit along Route 234 Business is 45 mph at its interchange with I-66.

US 29 (Centreville): US 29 is designated as a north-south route, but in the vicinity of I-66 in

Centreville, the roadway is oriented in an east-west direction. It is a four-lane divided roadway classified as an urban minor arterial south of its interchange with I-66 and a six-lane divided roadway classified as an urban principal arterial to the north. The posted speed limit is 50 mph south of the interchange with I-66 and 40 mph to the north.

Route 28: Route 28 is oriented in a north-south direction and is a six-lane divided roadway classified

as an urban principal arterial. It has a posted speed limit of 45 mph south of its interchange with I-66. North of I-66, the roadway transitions to a predominantly limited-access facility with a posted speed limit of 55 mph and connects with Route 7 at its northern terminus.

Stringfellow Road: Stringfellow Road is oriented in a north-south direction and is classified as an

urban minor arterial. A roadway construction project was completed in the summer of 2015 to increase the capacity of the roadway to the north of Fair Lakes Boulevard, widening the facility from two to four lanes. The I-66 interchange at Stringfellow Road operates as an HOV-only access point to and from the interstate during weekday peak periods. In October 2014, Stringfellow Road was configured as a four-lane divided roadway to the south of Fair Lakes Boulevard and a two-lane divided roadway to the north with a posted speed limit of 35 mph. This geometry is what is reflected in the existing conditions model.

Fairfax County Parkway: Fairfax County Parkway is oriented in a north-south direction and is

classified as an urban principal arterial. It is a four-lane divided roadway south of its interchange with I-66



and a six-lane divided roadway to the north. Arterials intersecting with Fairfax County Parkway immediately to the north and south of I-66 are grade-separated interchanges. The roadway is a regionally significant roadway between Route 7 to the north, I-95 and US 1 to the south. The posted speed limit is 50 mph at its interchange with I-66.

Monument Drive: Monument Drive is oriented in a northeast-southwest direction and is a four-lane

divided roadway classified as an urban minor arterial. It connects Fairfax County Parkway to the northwest with US 29 to the southeast. The posted speed limit along Monument Drive is 35 mph at its interchange with I-66. The I-66 interchange at Monument Drive operates as an HOV-only access point to and from the interstate during weekday peak periods.

US 50: US 50 is oriented in a northeast-southwest direction and is classified as an urban principal

arterial. It is a six-lane divided roadway north of its interchange with I-66 and a four-lane divided roadway to the south. US 50 provides an east-west travel route between the City of Fairfax and the City of Winchester and is roughly parallel to Route 7. The posted speed limit along US 50 is 45 mph north of I-66 and 35 mph to the south.

Route 123: Route 123 is oriented in a north-south direction and is a four-lane divided roadway

classified as an urban principal arterial. Route 123 is a primary arterial that links northern Arlington County at George Washington Memorial Parkway to southern Prince William County at US 1. The posted speed limit is 35 mph to the north of I-66, 30 mph to the south of I-66, and 45 mph through the interchange itself.

Vaden Drive: Vaden Drive is oriented in a north-south direction and is a four-lane undivided roadway

in the vicinity of its crossing with I-66. It is an unclassified, urban local roadway and has a posted speed limit of 25 mph. Vaden Drive passes over I-66 approximately 2 miles east of the Route 123 interchange and provides access to I-66 eastbound and from I-66 westbound via the Route 243 interchange. Vaden Drive provides access to Vienna Metrorail station parking garage facilities.

Route 243: Route 243 is oriented in a north-south direction and is classified as an urban minor arterial.

It is a four-lane divided roadway to the north of I-66 and a six-lane divided roadway to the south. Route 243 connects US 29 to Route 123 and provides direct access to the Metrorail Orange Line from I-66. The posted speed limit is 35 mph at its interchange with I-66.

I-495: I-495 is a major regional freeway, classified as an urban interstate, which circumnavigates

Washington, DC, through various cities and counties in Virginia and Maryland. At its interchange with I-66, access between the two interstates is provided in all directions, with the exception of westbound I-66 to northbound I-495 and southbound I-495 to eastbound I-66. Similar access between the two interstates is provided for general purpose and I-495 Express Lane movements. The posted speed limit along I-495 in the vicinity of I-66 is 55 mph within the general purpose lanes and 65 mph within the I-495 Express Lanes. Four general purpose travel lanes and two Express Lanes are provided in each direction.

Dulles Toll Road: The Dulles Toll Road is oriented in a north-south direction in the vicinity of I-66

and is a four-lane divided roadway classified as an urban freeway. The Dulles Toll Road is an east-west facility that begins at the Dulles International Airport. It is a four-lane divided roadway with the Metrorail Silver Line located in the median at its junction with I-66. At the I-495 interchange to the north, the roadway widens to provide four travel lanes in each direction, with the interior four lanes serving as a direct means of access to Dulles International Airport and the exterior four lanes serving as a means for



access to local roadways. Travel along the interior lanes is free, while travel along the exterior lanes requires payment of a toll in order to access the local roadways. The posted speed limit is 55 along the entire stretch of the Dulles Toll Road.

5.4 Alternative Travel Modes The Washington metropolitan area is comprised of a regional transportation network that experiences congestion on a daily basis associated with commuter trips. The I-66 corridor carries a significant volume of commuters from the western portions of the region into major employment hubs including Fairfax, Tysons, Arlington, and Washington, DC. A number of alternative travel modes are available to commuters that are geared toward reducing vehicular demand on the I-66 corridor and providing commuters with options and flexibility in meeting their personal transportation needs. The following sections summarize the existing alternative travel mode options for commuting along the I-66 corridor.

5.4.1 Regional Bus Service

Potomac and Rappahannock Transportation Commission (PRTC) PRTC is a multi-jurisdictional agency representing Prince William, Stafford and Spotsylvania Counties and the Cities of Manassas, Manassas Park and Fredericksburg. PRTC provides commuter bus service along the busy I-95 and I-66 corridors to points north (OmniRide and Metro Direct) and local bus services in Prince William County and the cities of Manassas and Manassas Park (OmniLink and Cross County Connector). Average ridership is approximately 13,000 passengers per day.

Fairfax Connector Fairfax Connector is a public bus service provided by Fairfax County. Eighty-five different bus routes within Fairfax County provide service to more than 180 square miles within the Washington metropolitan area (largely confined to Fairfax County). Average ridership exceeds 35,000 passengers per day. The system operates in conjunction with Metrobus and Metrorail through the use of the SmarTrip fare cards.

Metrobus Metrobus is a bus service operated by Washington Metropolitan Area Transit Authority (WMATA) covering an area of 1,500 square miles in the Washington metropolitan area. There are over 300 bus routes serving more than 12,000 stops. Average ridership exceeds 400,000 passengers per day.

City-University Energysaver (CUE) The City of Fairfax CUE bus system provides regularly scheduled, low-cost transportation services to George Mason University, shopping centers, and other locations within the City of Fairfax. Bus service is also provided to the Vienna Metrorail station. The system operates in conjunction with Metrobus and Metrorail through the use of the SmarTrip fare cards.

Privately-Owned Shuttle Buses Aside from the bus services listed above, a number of other private entities offer shuttle bus services within the Washington metropolitan area. Some of these services are geared toward transportation into and out of Washington, DC, while others operate local shuttle bus service. Fare collection and structures vary among the different providers. Many of these private shuttles routes are in close proximity to Metrorail, Fairfax Connector, and ART transit centers which provides a transfer opportunity to publicly operated bus and rail services.



5.4.2 Metrorail and Regional Commuter Rail

Metrorail Orange and Silver Lines Metrorail is a rail-based transit service operated by WMATA that provides transportation to more than 90 stations in Washington, DC, and the surrounding areas of Virginia and Maryland. Average ridership on the Metrorail system exceeds 700,000 passengers per day. The Metrorail Orange Line operates in the median of I-66 between the Nutley Street interchange in Vienna and Fairfax Drive interchange in Arlington before transitioning underground. The first station is the Vienna Metrorail station, followed by the Dunn Loring-Merrifield Metrorail station and the two Falls Church Metrorail stations, the latter two being located to the east of the I-495 interchange. Each of these stations provides between 400 and 5,000 daily parking spaces. The Metrorail Silver Line opened on July 26, 2014, and operates in the median of the Dulles Toll Road between Wiehle Avenue and I-66, with a diversion through Tysons to serve the four stations located along Route 7 and Route 123. The Metrorail Silver Line ties into the existing Metrorail Orange Line track network between the West Falls Church and East Falls Church Metrorail stations at the Dulles Connector Road interchange. Approximately 2,300 parking spaces are provided at the Wiehle-Reston East Metrorail station through WMATA and approximately 700 parking spaces are provided at the McLean Metrorail station through a third-party parking management company.

Virginia Railway Express (VRE) Manassas Line Virginia Railway Express (VRE) provides commuter rail service from the Northern Virginia suburbs to Fairfax County, Alexandria, Crystal City and downtown Washington, DC, along the I-66 and I-95 corridors. Altogether, the system operates 29 trains from 18 stations, providing transportation to approximately 19,000 passengers daily. In the vicinity of the I-66 corridor, the westernmost station is located near the interchange of Route 234 Bypass and Route 28 in Bristow, VA (approximately 4.5 miles from I-66). Three additional stations are located near the I-66 corridor in Manassas, Manassas Park, and Burke, VA. Between 600 and 1,500 parking spaces are provided for commuter use, free of charge, at each of the three stations.

5.5 Environmental Conditions and Constraints Information on environmental conditions and constraints is included in Chapter 12. Full details are shown in the Tier 2 Final Environmental Assessment.

During and after construction, pursuant to VDOT’s Road and Bridge Specifications, the construction contractor will be required to minimize disturbances of vegetation, habitat, and wildlife, as well as stormwater discharge, to adjacent land uses. The project has been aligned and is being designed such that disturbances of floodplains and water resources will be as little as practicable. In addition, the implementation of temporary and permanent stormwater management measures will reduce pollution of adjacent waterways to the extent practicable, and erosion will be mitigated with the application of stormwater management Best Management Practices (BMP).

5.6 Existing Data, Operational Performance, and Safety Conditions Detailed information on existing traffic volumes, traffic operations, and safety characteristics are included in Chapters 8, 9, and 10, respectively. The data in these chapters is shown as a baseline for the purposes of understanding future traffic operations and safety considerations under future scenarios.



CHAPTER 6. ALTERNATIVES CONSIDERED This section describes the proposed project, which generally involves constructing a two-lane Express Lane facility in each direction (four lanes total) within the median of I-66 between Haymarket (US 15) and I-495 while identifying the right-of-way needed within the median for future transit accommodations between the directional Express Lane facilities. As part of the proposed project, a minimum of three general purpose lanes will be provided in each direction, with auxiliary lanes provided between many system interchanges to facilitate access to and from I-66. Direct access to the Express Lane facility from intersecting roadways will be constructed at select locations along the corridor, many of which will provide access to park-and-ride and transit facilities. The no-action or No-Build Alternative is also discussed since it serves as a baseline for comparison.

6.1 Alternatives Development and NEPA Screening Process As part of the Tier 1 Environmental Impact Statement (EIS), a number of improvement concepts were developed to improve capacity along the I-66 corridor, including the following:

1. General purpose lanes 2. Managed lanes 3. Metrorail extension 4. Light rail transit (LRT) 5. Bus rapid transit (BRT) 6. Virginia Railway Express (VRE) extension 7. Improved spot locations and chokepoints 8. Corridor intermodal connectivity 9. Corridor safety improvements 10. Improvements in transportation communication and technology 11. System-wide and out-of-corridor improvements to Metrorail 12. Construction of/improvements to parallel facilities 13. Transportation Demand Management (TDM) 14. No-Build

The Tier 1 Record of Decision (ROD) provides information pertaining to the consideration of a combination of the above concepts, with the Tier 2 Environmental Assessment (EA) considering provisions for additional general purpose lanes, Express Lanes, and rapid bus service on the Express Lanes. Two Build alternatives were considered that accounted for the combination of the aforementioned improvements. They were designated as Alternative 2A and Alternative 2B. The principal difference between the two alternatives was in the width of the mainline cross section and the location of Express Lane access points. The Preferred Alternative is a hybrid of Alternative 2A and 2B. VDOT used the National Environmental Policy Act (NEPA) evaluation process to select the desirable elements of each alternative to carry forward as the Preferred Alternative. The Preferred Alternative is outlined in Section 6.4.

The development of improvements in this corridor followed a tiered NEPA evaluation process, which assisted with the selection of desirable elements of each alternative to carry forward as part of the Preferred Alternative. FHWA’s regulations implementing NEPA identify the types of actions that normally require an Environmental Impact Statement (EIS). The I-66 Tier 2 project is not a type of action that normally requires an EIS under that regulation. Instead, this project, which is along the existing I-66 corridor, falls under the category of actions for which an Environmental Assessment (EA) is the



appropriate document type. In addition, the preparation of a Tier 2 EA is consistent with the Council on Environmental Quality’s tiering provisions.

For the purposes of the environmental analyses, computations for construction “footprint” impacts have been prepared assuming a typical section along the I-66 corridor consisting of a transit reservation, two Express Lanes in each direction, and three general purpose lanes in each direction. Sufficient engineering has not yet been fully completed at this stage of project development to determine the exact finalized location of improvements within the median, the outer limits of the general purpose lanes, and at system interchanges. However, to illustrate what the actual impacts may be, computations have been prepared for the actual footprint identified in the conceptual plans. This approach not only provides a maximum impact estimate but also provides flexibility for design revisions, once more detailed design efforts are undertaken, without reopening the environmental analyses. In addition, the environmental analyses take into account areas of particular sensitivity, such as streams and wetlands, where conceptual design efforts have attempted to minimize impacts or where additional efforts may need to be made during final design to further minimize impacts at select locations.

6.2 No-Build Alternative The No-Build Alternative provides a baseline of conditions against which to compare the Build Alternative. Under the No-Build Alternative, the proposed Express Lanes would not be constructed and I-66 would remain in its present configuration, with two to three general purpose lanes in each direction and a peak directional HOV-3 lane between US 15 and I-495, functioning as an additional general purpose lane outside HOV-3 restricted hours. The No-Build Alternative also considers the variable use of a shoulder lane between US 50 and I-495 in the peak direction of travel. The existing Metrorail Orange Line service is within the median of I-66 and has access from the mainline just west of the Route 243 (Nutley Road) interchange where the rail service ends.

Most other existing roads would also generally remain in their present configurations. However, the Financially Constrained Long-Range Transportation Plans (CLRP) of the National Capital Region Transportation Planning Board contain a number of other projects funded for construction in the region. These were assumed to be in place by the design year (2040) and were taken into account in the road network assumed for traffic forecasting efforts of the future No-Build conditions for this project. Several of these projects would connect with or directly impact I-66 in the project corridor:

Vaden Drive Express Bus Access Ramp (constructed as a separate project if I-66 project did not advance)

Route 28 Widening to Westfields Boulevard (constructed as a separate project if I-66 project did not advance)

Fairfax County Parkway Widening Route 234 Bypass (Bi-County Parkway) US 29/Linton Hall Roadway Interchange Improvements US 15 Diverging-Diamond Interchange (DDI) I-66 Widening and concurrent HOV lane construction (Haymarket to US 29 (Gainesville))

In addition to projects providing improved access to I-66, a number of arterial improvements were considered to enhance traffic operations outside the I-66 corridor but within the project study area:

US 29 – Widen between Route 243 and I-495 City of Fairfax Intersection Improvements (US 50 at Jermantown Road, US 29 at Route 123)



Fairfax County Parkway Widening to 6 lanes and HOV operations between I-66 and the Dulles Toll Road

Stringfellow Road Widening Route 28 – Remove Traffic Signal at Ellanor C. Lawrence Park Braddock Road Extension crossing I-66 to the US 29 and Stone Road Intersection Route 234 Business and US 29 Eliminated through Manassas Battlefield Park Route 234 Bypass Interchange at Balls Ford Road

In addition to these transportation infrastructure improvements, additional capacity is being added to the Stringfellow Road park-and-ride lot by the County of Fairfax. The addition of 315 spaces to the existing 385 spaces is currently under construction.

6.3 TSM Options Transportation System Management (TSM) focuses on improving the operational efficiency of transportation systems without major system improvements (such as adding lanes or new ramps). Freeway TSM strategies can include signing and pavement striping improvements, traffic surveillance and control equipment, incident-management programs, HOV facilities, and ramp metering. Corridor and system-wide TSM strategies may incorporate improvements to mass transit service, multimodal facilities, and intelligent transportation systems.

Consistent with FHWA’s Interstate System Access Information Guide, Eight Policy Point Requirements, Point 2, TSM strategies were studied, many of which are already present on the existing I-66 Outside the Beltway corridor today:

I-66 already contains non-barrier-separated HOV lanes and two HOV interchanges (Monument Drive and Stringfellow Road). The lack of barrier separation for the HOV lanes, coupled with the lack of direct access from HOV lanes to most interchanges (HOV vehicles must cross three lanes of traffic to exit on the right side), result in less-than-optimal operations of the HOV lanes and transit service during congested periods.

I-66 has many existing park-and-ride lots, but many are at or above capacity and/or lack convenient access to the HOV lanes for commuter buses, carpools, and vanpools.

I-66 already has an Advanced Traffic Management System (ATMS) featuring traffic surveillance, incident management, and lane control signals.

I-66 Outside the Beltway corridor, even with the TSM strategies implemented above, experiences the operational and safety issues described in the Purpose and Need (Chapter 2). Due to the nature of the Purpose and Need of the project, TSM options alone will not address the system linkage and operational safety issues associated with the I-66 Corridor Improvements Project. A hybrid combination of TSM strategies and Alternative Transportation Modes was also insufficient to address the system linkage and operational safety issues associated with the corridor. However, the Preferred Alternative identified in this IJR incorporates several TSM strategies and Alternative Transportation Modes. These strategies include:

Express Lanes separated with flexible-post bollards for HOV-3+ vehicles and transit. New or expanded park-and-ride lots with direct access to the Express Lanes. New and improved transit service from park-and-ride lots to regional activity centers using the

Express Lanes. Geometric improvements to existing ramps and interchanges.



6.4 I-66 Tier 2 Build Alternatives (Express Lanes) Amid the improvement concept scenarios (ICSs) carried forward from the Tier 1 EIS to the Tier 2 Final EA, focus remained constant along the following improvement goals:

Reduce congestion on I-66 by increasing capacity; Provide new, predictable travel choices; Enhance safety and travel predictability; and Deliver innovative transportation solutions that are cost effective in a timely manner.

The conclusion of the Tier 1 EIS study determined the need to improve the I-66 corridor to at least a 10-lane divided highway with improved interchanges and additional direct access at certain locations to alleviate congestion and improve safety. Various configurations of a 10-lane facility with improved interchanges and additional access were developed, analyzed, and evaluated for this study.

The proposed project would begin west of US 15 in Prince William County near Haymarket. It would end at I-495, with a transition to the existing I-495 general purpose and Express Lanes at the I-495 interchange. The new facility would operate within the median of I-66 and consist of two-lane, limited-access Express Lanes in the eastbound and westbound direction.

6.4.1 Mainline Configuration Selection Mainline roadway configuration concepts/typical sections were narrowed down to two alternatives, Alternative 1 and Alternative 2.

6.4.1.1 Alternative 1 Alternative 1 consists of a 2-foot concrete barrier-separated section with 12-foot shoulders (total of 14 feet) and a 42-foot center median for potential future center transit, with auxiliary lanes providing ramp-to-ramp connections if needed. A total of four full shoulders would be provided in each direction. This typical section width is 266 feet from edge-of-shoulder to edge-of-shoulder, increasing to 290 feet with auxiliary lanes between interchanges.

6.4.1.2 Alternative 2 Alternative 2 has three configurations. Each configuration uses a 4-foot flexible bollard buffer-system to separate the Express Lanes from the general purpose lanes.

Alternative 2A consists of a 42-foot center median for potential future center transit and auxiliary lanes providing ramp-to-ramp connections, if needed. A total of two shoulders would be provided in each direction. The Express Lanes would have a full shoulder on the left and the general purpose lanes would have a full shoulder on the right. The Alternative 2A typical section width is 246 feet from edge-of-shoulder to edge-of-shoulder, including auxiliary lanes between interchanges.

Alternative 2B consists of no median, with a concrete barrier separating eastbound and westbound travel lanes, and auxiliary lanes providing ramp-to-ramp connections, if needed. The Alternative 2B typical section width is 206 feet from edge-of-shoulder to edge-of-shoulder, including auxiliary lanes between interchanges.

Alternative 2C is similar to Alternative 2A but provides space for future center transit extension stations by increasing the median width from 42 feet from Alternative 2A to 60 feet in the locations where future Metrorail stations are anticipated.



6.4.1.3 Selection of the Preferred Alternative The mainline alternatives were evaluated based on impacts to right-of-way, major utilities, and the environment, as well as safety implications, accommodation of future fixed-guideway transit, geometric design feasibility, traffic operations and relative cost.

Due to the significant right-of-way impact, Alternative 1 was eliminated from further engineering consideration by project stakeholders. Alternative 2C was eliminated after Alternative 2A was modified to include the median “bump outs” to provide for future Metrorail stations, resulting in Alternative 2C being a redundant alternative. Alternatives 2A and 2B were advanced for further analysis

Alternative 2A was selected as the typical section from Catharpin Road to I-495. The project extends to approximately Antioch Road, but from Antioch Road to Catharpin Road, the median is reduced and does not provide room for transit. This alternative was selected because it preserves the median for future expansion of median transit for the majority of the corridor. The Preferred Alternative typical section can be seen in Figure 6.1.

Figure 6.1: I-66 Mainline Typical Section

After further coordination with stakeholders, and FHWA, VDOT determined that the design will be phased. Phase 1 of the Preferred Alternative will reduce the initial project cost and reduce right-of-way impacts by deferring several elements of the project to a later phase. The typical section will be reduced to the Alternative 2B section from University Boulevard to just west of US 29 (Centreville). Under the Phase 1 configuration, University Boulevard will be the western-most access point of the project. There will be a transition zone between the Express Lanes and the single concurrent HOV lane in each direction, between US 29 (Centreville) and University Boulevard. The phased approach will apply to other interchanges as well. At Stringfellow Road and Monument Drive, existing median ramps will continue to be utilized under Phase 1, with some additional access improvements. This configuration will allow the existing bridges for Monument Drive and West Ox Road to remain, and will allow for deferred construction of a flyover ramp from Stringfellow Road to eastbound I-66 Express Lanes. The median will also be reduced at US 29 (Centreville) in order to preserve the existing I-66 bridges over US 29 (Centreville). Phase 1 does not preclude a median transit option in the future, but utilizes existing infrastructure in the median today. This phased approach will reduce project costs and allow more flexibility in future design, when the median transit option is more defined. VDOT is committed to implement the remaining elements of the Preferred Alternative by the year 2040, to the extent additional travel demand in the corridor



warrants, and will seek additional funding to implement needed improvements in conjunction with regional and state funding plans, and in coordination with the local jurisdictions.

6.4.2 Direct Express Lane Access Points and Crossovers Access points to and from the Express Lanes will be needed to implement the Express Lanes element of the project.

6.4.2.1 Access Locations Considered Twenty-one potential access-point locations were identified throughout the I-66 corridor. These access-point locations were compared against each other to determine which locations to carry forward in analysis and which to dismiss from further consideration. The 21 access-point locations considered were:

US 15 US 15 Slip Ramps (between US 15 and US 29 (Gainesville)) US 29 (Gainesville) University Boulevard Route 234 Bypass Balls Ford Road Park-and-Ride Lot Route 234 Business Slip Ramps between Route 234 Business and US 29 (Centreville) US 29 (Centreville) Route 28 Slip Ramps and Flyover Ramps between Route 28 and Stringfellow Road Stringfellow Road (east facing only) Fairfax County Parkway Monument Drive US 50 Slip Ramps between US 50 and Route 123 Route 123 Vaden Drive/Vienna Metrorail station Route 243 (Nutley Street) Dunn Loring Flyover Ramp (between Route 243 and I-495) I-495 (general purpose lanes and Express Lanes)

Travel demand model sensitivity testing was utilized to screen access-point locations throughout the I-66 corridor. If the access point demonstrated minimal demand, it was eliminated from further consideration. Geometric analysis also was conducted for access-point feasibility. If a fatal flaw was discovered, the access point was eliminated from further consideration. Following the evaluation of the 21 access-point locations, several were dismissed from further consideration. Fully-directional access for all movements was dismissed at Fairfax County Parkway. Direct connections were dismissed at:

US 15 US 29 (Gainesville) Route 234 Business US 29 (Centreville) Stringfellow Road to and from the west of the interchange US 50 to and from the west of the interchange Route 123 to and from the west of the interchange



Route 243 (Nutley Street)

Slip-ramp connections (between Express lanes and the general purpose lanes) were dismissed along the following segments of I-66:

Between Route 234 Business and University Boulevard (proposed in lieu of direct access to/from University Boulevard)

Between Route 234 Business and US 29 (Centreville) Between US 50 and Route 123 (proposed in lieu of direct access to/from US 50)

After determining the access-point locations for further consideration, possible geometric configurations were considered and evaluated at each interchange location. There are 11 existing interchanges with full movements and two interchanges with east-facing access to and from the existing I-66 HOV lanes, and seven new proposed access-point locations. Multiple interchange configurations were considered for:

Locations recognized as existing chokepoints; Locations with both general purpose lane and Express Lane access; and Locations with new Express Lane access only.

Connections to and from the Express Lanes are proposed at the following existing interchanges:

Route 28 to and from the east and west (excluding movements between west and south legs) US 50 to and from the east Route 123 to and from the east I-495 to and from the west

In addition to the existing interchanges, new interchanges are proposed to serve corridor traffic, via direct ramps to and from the Express Lanes, at the following locations:

Haymarket Park-and-Ride Lot to and from the east (By others through a separate, but coordinated project, with direct access by 2040)

University Boulevard to and from the east Route 234 Bypass to and from the west (Preferred Alternative, by 2040) Cushing Road Park-and-Ride Lot, to and from the east (Preferred Alternative, by 2040) Balls Ford Road Park-and-Ride Lot (proposed), between Groveton Road and Old Compton Road,

to and from the east Vaden Drive to and from the west

Several improvement concepts were developed for each interchange location using an incremental improvement approach to address safety, capacity, and operational requirements to minimize right-of-way, environmental, and cost impacts. The alternatives for Express Lane access were developed, varying in terms of access location and type (i.e. slip ramps or flyover ramps) between the general purpose lanes and Express Lanes, compared with direct-access ramps serving arterials. The remaining potential access-point locations were combined to derive the two draft access alternatives, Alternative 2A and Alternative 2B.

These Build alternatives were presented to the public at a series of public hearings in May and June, 2015. Elements of the two alternatives were then combined into one Preferred Alternative based on input from the public, coordination with stakeholders, traffic analysis, and mitigation strategies to eliminate or reduce potential environmental impacts. The Preferred Alternative is shown in the Functional Plans in Appendix B.



CHAPTER 7. ROADWAY GEOMETRY The Preferred Alternative was developed to a level of detail to support detailed cost estimates, right-of-way needs, and to confirm adherence to design criteria. Appendix B contains plans, profiles, typical sections, cross sections, geometric details, and other design information. The alignments reflect AASHTO design criteria for freeways. Table 7.1 summarizes design parameters.

Table 7.1: Design Parameters

Freeway Segment Design Speed Functional Classification Design-Year Traffic 2040 (vehicles per

day)

I-66 Express Lanes (US 15 to I-495)

70 Principal Arterial -

Interstate 75,800

I-66 General Purpose Lanes (US 15 to US 29 (Centreville)) 70

Principal Arterial - Interstate

180,000

I-66 General Purpose Lanes (US 29 (Centreville) to I-495)

60 Principal Arterial -

Interstate 233,600

7.1 Background The geometry of the Preferred Alternative reflects a number of key constraints and planning decisions. Foremost among these is the desire for the improvements to ‘not preclude’ the future extension of the Metrorail Orange Line. Aside from this regionally significant transit consideration, elements of future improvements that are considered in the context of a larger plan include the construction of the Bi-County Parkway to the north of I-66 and Route 234 Bypass, the widening of Route 28 between US 29 (Centreville) and Westfields Boulevard, the widening of Fairfax County Parkway, and transit access improvements at Vaden Drive.

For the purposes of understanding the geometric design elements of the project, a set of design plans is included by reference showing plans, profiles, cross sections, bridge structures, and retaining walls. Refer to Appendix B which shows conceptual design plans for the Preferred Alternative. Note that due to the volume of plan sheets in this plan set, Appendix B is incorporated by reference under separate cover.

7.2 Preliminary Engineering Development Several factors influenced the design of the mainline and of each interchange within the project corridor. These included access to transit, safety improvements, right-of-way acquisition in critical areas such as residential neighborhoods and parks, improved traffic flow and operations, geometric constraints, and project cost. After the Public Hearings in the spring of 2015 presenting Alternatives 2A and 2B, the team then selected one interchange configuration to advance to the Preferred Alternative based on input from citizens and VDOT. Alternative 2A was selected as the typical section from Catharpin Road to I-495. The project extends to approximately Antioch Road; however, the median is reduced and does not provide room for transit between the Antioch Road and Catharpin Road bridges. Even with this reduced median, this alternative was selected because it preserves the median for future expansion transit for the majority of the corridor. Each access point was considered independently and in combination with the other access points when evaluated for inclusion in the Preferred Alternative. Elements from each Build alternative were combined to develop a draft Preferred Alternative for additional evaluation. Additional design work continued after the Public Hearings to reduce impacts to adjacent properties. As a result of these efforts, property impacts were eliminated from Manassas Battlefield Historic District and Ellanor C.



Lawrence Park. They were also reduced at Stenwood Elementary. These conceptual designs were incorporated into the Preferred Alternative.

Each interchange began with several conceptual drawings. The team selected two concepts to advance to the Public Hearings as either Build Alternative 2A or Build Alternative 2B. In some cases, such as Route 28 and I-495, additional concepts were considered later as it became clear that neither Alternative 2A nor Alternative 2B would meet the design requirements. Interchanges concepts were selected for the Preferred Alternative based on public and stakeholder input. The designs were selected based on access, safety, right-of-way impacts, and traffic operations.

After further coordination with stakeholders, it was determined that the construction of improvements would be phased. Phase 1 of the Preferred Alternative will reduce the initial project cost and reduce right-of-way impacts by deferring several elements of the project to a later phase. The typical section will be reduced to the Alternative 2B section from University Boulevard to just west of US 29 (Centreville). University Boulevard will be the western terminus of the project. There will be an open section with a transition of the Express Lanes to HOV lanes west of University Boulevard. The phased approach will apply to other interchanges as well. At Stringfellow Road and Monument Drive, median ramps will continue to be utilized with some additional access improvements. This will reduce project costs with the ability to retain the Monument Drive and Stringfellow Road bridges until such time as rail transit is extended. This will also allow more flexibility of design including the development of an alternative typical section with less of a right-of-way impact. The median will also be reduced at US 29 (Centreville) in order to preserve the existing I-66 bridge over US 29 (Centreville). Phase 1 does not preclude a median transit option in the future but utilizes existing infrastructure in the median today. This phased approach will reduce project costs and allow more flexibility in future design when the median transit option is better defined. Further Preferred Alternative improvements will be brought online in coordination with the local jurisdictions.

7.3 Design Exceptions and Design Waivers Completion of Phase 1 and the Preferred Alternative requires approval of several design exceptions and design waivers. These are listed in Exhibit 7.1. The design exceptions include shoulder width reduction, non-standard horizontal and vertical curves, vertical clearance, and interchange spacing. The waivers included reduced ramp recovery areas, vertical grades on ramps, and reduced buffer strips adjacent to shared-use paths. Most design exceptions occur at spot locations, although some occur over significant lengths of highway such as the design exception for no shoulder width on the left of the general purpose lanes and to the right of the Express Lanes due to the need for a 4-foot buffer with pylons between the general purpose and Express Lanes.

FHWA has not reviewed or approved any of the proposed design exceptions and waivers at the time this IJR was prepared.



CHAPTER 8. TRAFFIC VOLUMES This section provides a broad overview of the assumptions and procedures used for travel demand modeling and post-processing of modeling results for the traffic analysis.

8.1 Traffic Forecasting Methodology

8.1.1 Travel Demand Modeling Methodology and Key Assumptions Demand forecasts were developed for the I-66 corridor using the macroscopic travel demand model developed for this study in CUBE. The I-66 corridor model was based on the MWCOG/TPB model version 2.3, Build 52, and included strategic modifications to improve the forecasting for the corridor and increase the detail of the network representation of the highway and transit system. Ramps on I-66 were micro-coded to better represent the movements at the interchanges and align with the microsimulation process. The I-66 model was run with the MWCOG adopted land use version 8.3 for 2015, 2025, and 2040. The model network files were coded to reflect future No-Build and Build conditions, which included updates to the network to represent new projects added to the Constrained Long-Range Transportation Plan (CLRP) as well as more detailed link coding of geometry changes in the I-66 study area. Subsequently, transit files were updated to reflect the modified networks. Travel demand model runs were performed for future No-Build and Build scenarios to be able to compare traffic assignments to the existing conditions travel demand model assignments. Table 8.1 displays travel demand modeling assumptions for this project.

Table 8.1: Travel Demand Modeling Assumptions

Assumption Base Case Comments Model Analysis Years: 2015 2025 2040

MWCOG/TPB Model: 2015 2025 2040

Aligned with MWCOG/TPB model forecast year.

Time Periods Modeled

Two time periods representing:

Period Hours AM 6 a.m. – 9 a.m. PM 3 p.m. – 7 p.m.

Hours for time-of-day periods for traffic assignment in MWCOG/TPB model version 2.3.

Speeds Consistent with current posted speed limits in the HOV and GP lanes.

Consistent with existing conditions.

Link Capacity Link capacities are defined consistent with the MWCOG/TPB model approach.

The MWCOG facility and area type capacity tables are used to determine link capacities.

Peak Spreading Peak Period to Peak Hour factors: Existing peak-period values were derived from the 2007/2008 MWCOG Household Travel Survey. The peak hour factors decline in future years in recognition of the increased congestion expected in the region. This assumption spreads the traffic evenly over the entire peak period.

Developed using MWCOG spreading factors in conjunction with existing counts at each interchange.



Assumption Base Case Comments

Period 2015 2025 2040 AM 0.417 0.38 0.34 PM 0.294 0.272 0.25

Value of Time (VoT) The VoT is based on the Tier II Traffic & Revenue study toll diversion curves developed for Office of Transportation Public and Private Partnerships (OTP3).

Land Use MWCOG/TPB version 8.3 Land-use assumptions in place for individual model forecasts.

Network Assumptions General MWCOG/TPB version 2.3, Build 52, with

changes relating to current TIP and CLRP publications.

Project Description (I-66 Express Lanes)

• Two HOV-3+/Express Lanes in each direction between I-495 and Haymarket.

• Reconfiguration of several interchanges.

Consistent with revised CLRP submission.

Project Extent West of US 15 to east of I-495. Consistent with revised CLRP submission.

I-495 and I-95 • Express Lanes in both directions on I-495 from 2013.

• Reversible Express Lanes on I-95 from 2014.

Consistent with the I-495 and I-95 projects.

HOV • HOV restrictions on area roadways under existing conditions consistent with restrictions in 2015.

• All HOV facilities in Virginia are assumed to become HOV-3+ by opening year.

I-66 Inside Beltway • Under existing conditions, restricted to HOV-2+ vehicles inbound (eastbound) for the AM peak period and outbound (westbound) for the PM peak period.

• Under future conditions (2025 and 2040), restricted to HOV-3+ and HOT vehicles in both directions in the AM and PM peak periods.

For the purposes of this study, tolling is assumed in both directions during the AM and PM peak periods. The analysis was completed before an official decision was made on the extents of tolling.

Toll Assumptions Tolling Methodology Toll Diversion Curves (TDC)

Toll Approach Variable toll rates by roadway segment, based on maintaining managed lane speed goal of 55 mph.

Adopted to account for varying demand levels along the length of the project.

Tolls

• Minimum toll rate: $0.25/mi.



Assumption Base Case Comments

Mode Assumptions Vehicle Class • HOV-3+: Free

• Other Cars: Tolled

• Trucks: Banned

Consistent with project definition.

HOV Vehicles Modeled using the TPB Model HOV module. The HOV estimates provided are an output of the mode choice and carpool occupancy models developed by MWCOG.

Hybrid/Violators Hybrids and violators are not explicitly modeled in the Express Lanes. Hybrids will not be granted special exemptions to use the lanes toll-free. Experience on the I-95 Express Lanes has shown that enforcement of violators reduces violation rates to approximately 1%.

Buses In-service buses are assigned to the network using the Express Lanes where appropriate. Non-revenue service buses are not assigned to the network.

Transit Capacity Constraint

MWCOG 2020 Core Capacity constraint is not used in these runs to understand the total demand for transit service.

8.1.2 Methodology/Key Assumptions for Post-Processing of Modeling Results

Post-processing of travel demand model output was necessary to analyze traffic operations during representative-hour conditions using peak period model outputs. Post-processing followed NCHRP 255 guidelines for estimating balanced existing, No-Build, and Build peak-hour volumes.

Extensive data collection occurred in early June 2014. This included:

• 24-hour traffic counts with vehicle classifications at all ramp locations within the study area and along the mainline of I-66 and I-495.

• AM and PM peak-period turning-movement counts. Counts generally occurred between 5:00 a.m. and 10:00 a.m. for the morning peak period and between 3:00 p.m. and 8:00 p.m. for the evening peak period.

• Travel time runs along the entire corridor for the AM and PM peak periods. This information, along with INRIX travel time data for I-66, I-495, and Route 28, was used to identify where ramp counts may be constrained by mainline congestion.

Table 8.2 outlines the steps for estimating existing, No-Build, and Build representative-hour volumes.



Table 8.2: Traffic Volume Estimation Steps

Step Description

Existing Peak-Hour Volumes 1 Collect, compile, and review raw count information (ramps, mainline, and intersections). 2 Check for suspect/bad count data. 3 Calculate system peak hours. 4 Review volume-time profile to check the congestion-constrained locations. 5 Use demand smoothing adjustments. 6 Balance adjustments. 7 Produce final rounded and balanced 2014 peak-hour volumes.

No-Build Peak-Hour Volumes 1 Pull peak period assigned volumes from the existing travel demand model and future No-

Build travel demand model to calculate a raw delta and growth factor between the years for each link.

2 Estimate future-year peak-period volumes by growing existing balanced volumes using the raw delta. If the calculated future-year volume is more than 300% of the existing volume or less than 50% of the existing volume, use the growth factor instead of the raw delta to perform this calculation. If the resulting future volume is still greater than 300% of the existing volume or less than 50% of the existing volume, cap the increase/decrease at this amount. Perform manual review on cases where this cap may be lifted; for example, in the case of a new link, such as the University Boulevard southern extension, the volume can grow by more than a factor of 300%.

3 Along freeway and ramp links, apply smoothing factors for half-hour intervals and balance along the length of the corridor.

4 At arterial intersections, convert future link volumes to turning movements by using the iterative-directional method described in NCHRP 255. Note that any intersection with a freeway ramp should use the balanced ramp target from Step 3.

5 Balance between intersections where needed. 6 Review balanced volumes and produce final rounded and balanced 2025 and 2040 peak-

hour No-Build volumes. Build Peak-Hour Volumes

1 Pull peak-period assigned volumes from the No-Build travel demand model and corresponding year Build travel demand model to calculate a raw delta and growth factor between scenarios for each link.

2 Similar to Step 2 for No-Build peak-hour volumes, calculate future Build volumes by adding the raw delta or growth factor to the No-Build volume, subject to a cap of not increasing by greater than 300% or decreasing by more than 50%.

3 Along the freeway and ramp links, apply smoothing factors for half-hour intervals and balancing along the length of the corridor.

4 At arterial intersections, convert future link volumes to turning movements by using the iterative-direction method described in NCHRP 255. Note that any intersection with a freeway ramp should use the balanced ramp target from Step 3.

5 Balance between intersections where needed. 6 Review balanced volumes and produce final rounded and balanced 2025 and 2040 peak-

hour Build volumes.



Table 8.3: Traffic Volume Post-Processing Assumptions

Elements Assumption

System-wide peak period 5:00 to 10:00 a.m. 2:30 to 7:30 p.m.

System-wide peak hours for developing balanced hourly volumes

AM Pre-Peak: 5:30 a.m. to 6:30 a.m. AM Peak: 7:00 a.m. to 8:00 a.m. AM Post-Peak: 9:00 a.m. to 10:00 a.m. PM Pre-Peak: 3:00 p.m. to 4:00 p.m. PM Peak: 5:00 p.m. to 6:00 p.m. PM Post-Peak: 6:30 p.m. to 7:00 p.m.

Peak period to peak hour factors Vary by interchange.

Ramp capacity Varies by ramp type, interchange, and downstream conditions.

Vehicle classifications Derived from MWCOG/TPB model screenlines in conjunction with existing classification data.

8.2 Traffic Analysis Scenarios The operational performance of the I-66 project was evaluated for three analysis years: existing conditions (2015), opening year (2025), and design year (2040). Construction for the project is expected to start in 2017 and be completed in 2021. The analysis includes No-Build and Build conditions in both 2025 (opening year) and 2040 (design year).

The traffic demands used for the analysis of all scenarios were developed using the methods described in Section 8.1. The traffic demands used in the operational analysis for each roadway section for existing, No-Build, and Build scenarios are shown in Appendix A of the I-66 Transportation Technical Report.



CHAPTER 9. TRAFFIC ANALYSIS Traffic analyses were performed for the AM and PM peak periods for three analysis years: existing conditions (2015), 2025, and 2040. Construction for the project is expected to begin in 2017 and be completed in 2021. This analysis includes No-Build and Build conditions in both 2025 and 2040. In 2025, the Build conditions are analyzed using the Phase 1 design concept. In 2040, the Build conditions are analyzed using the Preferred Alternative design concept.

Federal Highway Administration (FHWA) policies on IJR analysis methodology and documentation recommend traffic operational analysis using the Transportation Research Board’s 2010 Highway Capacity Manual (HCM) methodologies. Typically, this analysis would be conducted using Highway Capacity Software (HCS), which is based on the HCM procedures and assesses freeway, weaving, and ramp operations. This deterministic software provides a macroscopic view of traffic operations and can be used for air quality analysis. Per discussion with FHWA Headquarters, it was recognized that HCS has limitations in analyzing oversaturated highway systems in urban areas. Thus, the preferred tool for traffic analysis in this study was a microsimulation analysis using the VISSIM software. VISSIM is able to account for system-wide operations, including upstream and downstream conditions at any roadway segment.

The purpose of traffic simulation modeling for this project was to evaluate the operational effects of the Phase 1 and Preferred Alternative configurations for I-66 west of I-495. VISSIM stochastically simulates traffic operations for individual vehicles on freeway segments and provides traffic operational data including vehicle delay, density, and travel speeds on freeway networks. VISSIM reports average density as vehicles/mile/lane, and density analysis results are depicted in similar levels of congestion to the HCM density-based level of service thresholds. For the local surface street intersections, Synchro software was used to help determine future traffic signal configurations and settings for optimized intersection and arterial traffic operations. However, Synchro software was not used to report operational analyses for arterial intersections. The analyses were reported using a signalized intersections methodology similar to that contained in the HCM and based on average delay per vehicle and queue length obtained from the VISSIM software, which reports intersection operations based on the movements of individual vehicles. Detailed Traffic Output (VISSIM) is provided in Appendix C and in digital format on CD. Traffic input files are also included.

Exhibits 4.1 and 4.2 (Chapter 4) show the various components of the project study area. The figures are color-coded as follows:

Green – IJR Study Area. This area represents the footprint of I-66 west of I-495 and extends from just west of US 15 to just east of I-495. It also includes Route 28 from north of Westfields Boulevard to south of I-66.

Yellow – IJR Area of Influence. This area represents the extent of traffic analysis in VISSIM and includes the entire IJR Study Area plus additional freeway and arterial segments. The area of influence extends from west of Old Tavern Road to east of the Dulles Toll Road. It includes several interchanges along I-495, extending from north of the interchange with Route 7 to south of the interchange with Gallows Road. At each interchange along I-66 and I-495, the traffic analysis encompasses affected unsignalized and signalized intersections in the vicinity of I-66 as determined by engineering judgment.



9.1 Microsimulation Methodology The primary tool used for the microsimulation analysis in the IJR was the PTV VISSIM microsimulation traffic package. VISSIM is a microscopic, behavior-based multimodal traffic simulation program. VISSIM was used to simulate traffic operations along the I-66 corridor, including mainline segments, ramps, interchanges, and freeway connections. The traffic simulations also encompassed arterials at interchanges and adjacent intersections.

A key benefit of the VISSIM analysis package is the ability to visually simulate traffic operations to reveal the operational effects of various design solutions.

The VISSIM study area encompasses the entire IJR area of influence. The model results for this IJR were based on the model outputs for links and nodes (intersections) within the area of influence. The analysis network for the I-66 corridor VISSIM microsimulation is larger and more complex than the networks for most simulation efforts. The key variables for a simulation are the number of vehicles, the size of the network (number of links and/or intersections), the level of congestion, and the duration of the analysis period. The I-66 corridor microsimulation study is more complex with regards to most of these measures, especially for the level of congestion (10 to 12 hours on a weekday in several sections of the corridor) and high freeway traffic volumes. The following sub-sections detail the steps taken to replicate these complex operations.

Origin-Destination (O-D) Synthesis Using VISUM An important component of VISSIM modeling is the development of origin-destination (O-D) patterns which reflect regional travel patterns and are consistent with field traffic counts. To create these patterns for individual vehicle trips in the VISSIM microsimulations, the following processes were conducted:

1. A “focus model” of the project area was developed using the Metropolitan Washington Council of Governments (MWCOG) regional travel demand model as a base1, with refinements made within the I-66 study area to provide more localized detail. These included highway network modifications, transit network modifications, traffic analysis zone splits, and centroid connector location changes. The modified regional model also employed a toll diversion curve algorithm to forecast managed lane trips. This macroscopic modeling effort was conducted using Citilabs’ CUBE software.

2. A subarea cordon model was extracted from the regional model with subarea-specific trip tables treating trips entering and leaving the study area as entries and exits. This subarea model was imported into PTV VISUM mesoscopic modeling software, and the O-D matrices were used as seed matrices for mesoscopic modeling. Freeway and ramp demand estimates and turning movement count estimates were also imported into VISUM for the AM and PM system representative hours. Within VISUM, a more detailed roadway network was coded on top of the subarea model for the purposes of mesoscopic traffic assignment. VISUM utilizes a matrix estimation method called TFlowFuzzy to adjust a given seed O-D matrix (coming from the subarea cordon model) in such a way that the result of the traffic assignment closely matches observed volumes at points within the network.

3. Upon reviewing the results of the TFlowFuzzy process in VISUM, R-square statistics indicated an extremely good fit between the input and modeled volumes. These resulting TFlowFuzzy O-D matrices and path sets were transferred into the VISSIM microsimulation network. Separate path

1 The I-66 model used Version 2.3, Build 52 of the MWCOG travel demand model.



sets were developed for various vehicle classes, including general purpose automobiles, trucks, HOV, and HOT.

VISSIM Calibration of the Existing Conditions Models

Purpose of Calibration

Simulation models are an efficient tool for evaluating the effects of improvement alternatives, but it is well-established that the base model must first match real-world conditions. VISSIM, like all simulation models, was designed to be flexible enough that an analyst can calibrate the network to match the local conditions at a reasonably accurate level. FHWA has published “Guidelines for Applying Traffic Microsimulation Modeling Software” as part of its Traffic Analysis Toolbox (available at http://ops.fhwa.dot.gov/trafficanalysistools/index.htm). This document provides guidelines for microsimulation analysis, including guidelines for comparing model outputs to field data. The I-66 project team used these guidelines, as well as the current version of the Virginia Department of Transportation (VDOT) Traffic Operations Analysis Tool Guidebook (TOATG), to develop the calibration criteria outlined in this section.

Simulation Seeding Period

The seeding period is the period the model requires for the network-wide volumes to become stable. The length of the seeding period depends on numerous network factors, such as the size of the network and level of congestion. A seeding step is needed to ensure that output data is not collected until the end of the seeding period is reached. If it is collected earlier, simulation measures (e.g., travel time and congestion) may be under reported.

To determine the seeding period for the VISSIM simulation, two criteria were used:

The time it takes a single vehicle to traverse the entire corridor during the peak hour. Volume loading analysis.

For the first criteria, the time required for a vehicle to traverse the entire corridor was based on field travel time runs. Average times measured to travel the length of the corridor in the peak direction vary between 58 and 65 minutes in the AM and PM peak period respectively. For the second criteria, 10 simulation runs were made, with the total volume in the network reported every 2 and a half minutes. Results indicated that volumes in the network grew steadily during the first 35 minutes of the simulation before transitioning to stable conditions with normal increases and decreases for the rest of the simulation. As a result of these two analyses, a seeding period of one hour was found to be adequate for both the AM and PM models.

Number of Model Runs

Appendix B of the FHWA guidelines provides a summary of the need for multiple runs with a microsimulation model: “Multiple repetitions of the same model are required because microsimulation results will vary depending on the random number seed used in each run. The random number seed is used to select a sequence of random numbers that are used to make numerous decisions throughout the simulation run. The outcome of all of these decisions will affect the simulation results. The results of each run will usually be close to the average of all of the runs; however, each run will be different from the other.” The FHWA’s recommended approach to determine the number of runs is to determine a confidence interval for parameter(s) of interest. In this way, a number of runs can be calculated using the standard deviation of the parameter of interest and Student’s t-statistic for the confidence interval.

http://ops.fhwa.dot.gov/trafficanalysistools/index.htm

http://ops.fhwa.dot.gov/trafficanalysistools/index.htm



For the I-66 corridor study, this calculation was made more complex due to the desire to examine multiple parameters of interest (such as different volumes and travel time comparisons). The standard deviation of several key parameters was obtained by making 10 preliminary runs of the VISSIM model. The key parameters were as follows:

Average end-to-end travel time (AM peak period) for eastbound I-662. Average end-to-end travel time (AM peak period) for westbound I-66. Peak period volume on eastbound I-66 mainline between US 15 and US 29. Peak period volume on eastbound I-66 mainline between Route 28 and Fairfax County Parkway. Peak period volume on eastbound I-66 mainline between Route 243 and I-495. Peak period volume at the same locations in the westbound direction.

The confidence intervals assumed a 99 percent level of confidence and were calculated as follows:

Volumes: +/- 10 percent of the sample mean at each of the above locations. Travel time: +/- one Field Standard Deviation for the entire segment.

Based on the results obtained from the above methodology, it was concluded that 10 runs were sufficient to achieve the level of accuracy and variability in the model based on the adopted criteria.

General Approach for Calibration

Given the magnitude and complexity of the I-66 corridor simulation model, multiple measures of performance needed to be applied to calibrate the model. In the peak direction (eastbound in the AM and westbound in the PM), I-66 operates with the characteristics of an oversaturated facility for most of the peak period and for lengthy portions of the corridor. Oversaturated conditions make calibration extremely challenging since travel speeds and other measures can change rapidly in response to small changes in traffic demand. The length of the corridor (approximately 36 miles, inclusive of the area of influence) is another significant contributor to the complexity of the calibration task. The calibration of existing conditions for the I-66 corridor should be considered to have gone beyond what is the standard of practice for transportation projects. The effort included calibration of not only a single AM and PM peak hour but for the entire analysis period including the peak period and hours before and after the peak period in order to cover the variations in lane restrictions affecting operating conditions along the corridor.

The following measures were used for the calibration:

Route choice: measured through goodness of fit between travel demand model seed matrix and VISUM final assignment.

Mainline travel times: measured for the entire corridor (both directions) and between consecutive interchanges.

Traffic flow rates: measured for the entire corridor and for aggregated portions of the corridor for both mainline and ramps and compared with traffic counts through the GEH statistic index, R-square, and the Root Mean Square Normalized Error (RMSNE).

Travel speeds: measured on the mainline along the corridor every half mile and compared to INRIX data.

2 These travel times may slightly differ from the overall travel times shown in the calibration results because these calculations were done at an interim phase and before the final calibration of the models. However, the values used for the calculation of the number of runs are still valid.



Ramp and intersection queue lengths: compared to available aerial survey of the Metropolitan Washington region’s freeway system during the AM and PM peak periods prepared by SkyComp, Inc.

Bottleneck locations, length, and duration of backups: compared to INRIX data and field visual inspections.

Calibrating the I-66 corridor microsimulation study model occurred in three stages. The first stage involved calibrating the model route choice for the simulation period. This stage was done using the VISUM model as explained in previous sections. The second stage included calibrating the VISSIM model to data collected in the field including freeway and arterial traffic volumes, freeway travel times, INRIX travel speeds, and ramp and mainline queues (bottleneck locations, extent, and duration of backups). The final step was a visual audit of the simulation model by VDOT and the I-66 project team.

Calibration Results

The following section highlights the results of calibration for the I-66 AM and PM existing conditions models according to the previously described measures. The objective of model calibration is to achieve adequate reliability or validity of the model, by establishing suitable parameter values, so that the model simulates field conditions as closely as possible. The calibration was carried out using multiple (3 tiered) parameters: capacity, travel times and speeds. For large scale models, such as the I-66 VISSIM model, it can be difficult (or even impossible) to meet all calibration criteria, since changes to better match one particular parameter will impact the other parameters. Detailed results are provided in the Existing Conditions Technical Report.

AM Existing Model For travel times, all calibration targets are met for the general purpose lanes for all the eastbound

segments. The travel time of the general purpose lanes for the entire corridor is within 5 percent of the field travel times. In the westbound direction, all segments met the calibration targets.

In the eastbound direction, 84 percent of the segments’ simulated throughput volumes meet the GEH criteria in comparison to balanced traffic counts. This is very close to the target of 85 percent. More than 88 percent of links meet the volume differential target criteria. Intersection approach volumes were also compared to traffic counts for both GEH and volume difference criteria. Ninety percent of approaches meet these criteria. In order to focus the amount of time and effort spent on calibrating a model to within a reasonable range, and to meet a balance of parameters simultaneously, it was determined that a value of 84 percent of the segments meeting GEH for simulated throughput volumes was appropriate, based on previous coordination with VDOT and FHWA.

Average speeds were compared to INRIX speeds collected for similar days when traffic data was collected in the field. In the eastbound direction, almost 80 percent of links meet the criteria for comparison; while in the westbound direction and along I-495, more than 85 percent of the links match the criteria. Variation on individual segments in comparison to INRIX data can be expected for a variety of reasons.

In terms of specific bottleneck locations, length, and duration of backups, travel speeds measured every half mile and every 15 minutes in the model were compared to INRIX data. There is a very reasonable match between the spatial and temporal distributions of speeds from INRIX and from the VISSIM model results.



PM Existing Model For travel times, all calibration targets are met for the general purpose lanes for all the westbound

segments. The travel time of the general purpose lanes for the entire corridor is within 3 percent of the field travel times. In the eastbound direction, the difference in travel time for the entire corridor is within 1 percent.

In the westbound direction, 85 percent of the segments’ simulated throughput volumes meet the GEH criteria in comparison to balanced traffic counts, meeting the target. Additionally, 85 percent of links meet the volume difference criteria. Intersection approach volumes were also compared to traffic counts for both GEH and volume difference criteria. Over 90 percent of approaches meet these criteria.

Average speeds were compared to INRIX speeds collected for similar days when traffic data was collected in the field. In the westbound direction, approximately 81 percent of links meet the criteria for comparison; while in the westbound direction, more than 85 percent of the links match the criteria. Variation on individual segments in comparison to INRIX data can be expected for a variety of reasons.

In terms of specific bottleneck locations, length, and duration of backups, travel speeds measured every half mile and every 15 minutes in the model were compared to INRIX data. There is a very reasonable match between the spatial and temporal distributions of speeds from INRIX and from the VISSIM model results.

9.2 Traffic Operational Analysis Findings

9.2.1 Existing Conditions

Existing AM Peak Freeway Operations Figure 9.1 (a, b, c, and d) illustrates the density results from the VISSIM models for the I-66 mainline segments of the entire corridor for the AM peak period. In Figure 9.1, the centerline diagram laid over the aerial depicts the average density for the mainline segment during the representative hour (7:00 a.m. to 8:00 a.m.) in both the eastbound and westbound directions. The average densities are color coded based on the congestion levels as depicted in the legend. The boxes on the top and bottom depict the densities in each direction for the entire peak period including the shoulder periods before and after the peak period (6:00 a.m. to 10:00 a.m.). More detailed speed and density outputs for each basic freeway, ramp junction, and weave segment are contained in Appendix J of the Transportation Technical Report.

Existing AM Density

In the AM peak period, use of the shoulder lane is permitted in the eastbound direction. It can be seen from the exhibits that the eastbound segment between Route 234 Bypass and I-495 operates primarily under congested conditions during the entire peak period. The congestion starts west of the Route 243 (Nutley Street) interchange and continues to the Fairfax County Parkway interchange. This entire segment operates under congested to severely congested conditions for the entire peak period. At the interchange of Route 28, there is another bottleneck along I-66 eastbound which spills back to the Route 234 Bypass in the early hours of the peak period; and by the end of the peak period, congestion diminishes to east of the Route 234 Business interchange. West of the Route 234 Bypass, there is no congestion in the eastbound direction.

In the westbound direction, the segment between I-495 and US 50 operates under moderate to heavy congestion levels from 7:00 a.m. to the end of the peak period. The use of the shoulder lane is not



allowed for the westbound direction during the AM peak period. Beyond US 50, there is no congestion in the westbound direction.

Existing AM Speeds

Average speeds under existing conditions show similar patterns as seen from the density diagrams. Average speeds in the eastbound direction start to break down from west of the Route 123 interchange up to the Fairfax County Parkway interchange. Average speeds in this segment are below 35 mph with some segments operating at below 20 mph (queue condition). The speeds again drop to below 35 mph west of the Route 28 interchange. West of the Route 234 Bypass interchange, average speeds are similar to free-flow speeds. In the AM peak period, the leftmost lane in the eastbound direction operates as an HOV-only lane. However, the HOV lane is not a barrier-separated lane; hence, the average speeds reported by VISSIM include this lane which generally travels at a faster speed.

In the westbound direction, the average speeds range from between 50 to 60 mph east of the US 29 (Centreville) interchange. West of that, the westbound I-66 corridor operates under free-flow conditions.



Figure 9.1: I-66 Corridor – Existing Conditions AM Peak Period Densities (veh/ml/ln)



Figure 9.1b: I-66 Corridor – Existing Conditions AM Peak Period Densities (veh/ml/ln)



Figure 9.1c: I-66 Corridor – Existing Conditions AM Peak Period Densities (veh/ml/ln)



Figure 9.1d: I-66 Corridor – Existing Conditions AM Peak Period Densities (veh/ml/ln)



Existing AM Travel Time

Average travel time for segments and cumulative travel time for the corridor establish a baseline for comparison against future alternatives; travel time was also an important measure during the calibration process as previously discussed. Figure 9.2 shows segment and cumulative travel times for general purpose and HOV lanes for the eastbound direction during the AM peak period. The total average travel time to traverse the entire corridor from Old Tavern Road to Dulles Toll Road is 64 minutes and 42 minutes for general purpose and HOV, respectively. Segments identified in the density and speed analysis with the most congestion translate into greater travel time benefits for HOV compared against general purpose traffic.

Figure 9.2: Existing AM Time Travel for I-66 Eastbound

Existing AM Peak Intersection Operations During the AM system representative hour (7:00 a.m. to 8:00 a.m.), most intersections operate at adequate levels of service (LOS). Table 9.1 lists the intersections that operate at LOS E or worse during the AM system representative hour. Figure 9.3 summarizes both the actual number of intersections and the percentage with respect to the total grouped by LOS A to D, LOS E, and LOS F. As shown in this figure, approximately 8 percent of the intersections operate at LOS E, while 3 percent operate at failing conditions of LOS F. It is important to note that while many of these intersections operate at adequate overall control LOS, many of the individual approaches operate at failing conditions. See Appendix I of the Transportation Technical Report for approach intersection delay and LOS.



Table 9.1: Existing Conditions AM Intersections with LOS E or LOS F (7:00 – 8:00 a.m.)

Figure Intersection

ID* Intersection Name

Intersection Delay

(Sec/veh) LOS

15 Route 234/Balls Ford Rd 61.7 E


21 US 29/Stone Rd 65.8 E

24 US 29/I-66 EB Ramps 124.7 F

42 US 50/Waples Mill Road 94.0 F

44 Route 123/Jermantown Road 71.9 E

47 Route 123/Fairfax Blvd (Route 50/US 29) 63.4 E

57 Route 7/Idylwood Road 70.3 E

82 Gallows Road/I-495 Express Lanes Ramps 78.0 E * Intersection ID can be found in Appendix I of the TTR

Figure 9.3: Existing AM Representative Hour Intersection LOS Summary

Existing PM Peak Freeway Operations Figure 9.4 (a, b, c, and d) illustrates the density results from the VISSIM models for the I-66 mainline segments of the entire corridor for the PM peak period. In the PM peak, westbound I-66 is the peak direction with heavily congested segments and reductions in travel speeds. The leftmost lane is restricted to HOV-only traffic, and the use of shoulder lane is permitted in the westbound direction. Similar to AM peak, the centerline diagram in Figure 9.4 depicts the average density for the mainline segment during the representative hour (4:30 p.m. to 5:30 p.m.) in both the eastbound and westbound directions. The boxes on the top and bottom depict the densities in each direction for the entire peak period from 3:30 p.m. to 7:30 p.m. More detailed speed and density outputs for each basic freeway, ramp junction, and weave segment are contained in Appendix J of the Transportation Technical Report.



Existing PM Density

In the PM peak period, it can be seen from the exhibits that in the westbound direction, there is severe congestion from US 50 that spills back to the I-495 interchange throughout the peak period. Further west, the congestion at the Route 234 Business interchange starts to spill back at the beginning of the representative hour, reaching the US 50 interchange by the end of the peak period. West of the Route 234 Business interchange and inside I-495, I-66 westbound operates at acceptable vehicle density levels.

In the eastbound direction, all travel lanes are open, but the shoulder lane is closed for travel. Except for a few pockets between I-495 and US 50, which operate under heavy or congested conditions, all other segments along I-66 eastbound operate under light to moderate density levels.

Existing PM Speeds

Average speeds under existing PM conditions show similar patterns as seen from the density diagrams. Average speeds in the westbound direction start to break down from just west of the US 50 interchange to the I-495 interchange at the beginning of the peak period. Average speeds in this segment are below 35 mph with some segments operating at below 20 mph (queue condition). In the later hours of the peak period, the speeds again drop to below 35 mph east of the Route 234 Business interchange up to US 50. West of the Route 234 Business interchange, average speeds are similar to free-flow speeds. In the PM peak period, the leftmost lane in the westbound direction operates as an HOV-only lane, and since the HOV lane is not a barrier-separated lane, the average speeds reported by VISSIM include this lane which generally travels at a faster speed compared to the other lanes.

In the eastbound direction, the average speeds range from between 50 to 60 mph east of the US 29 (Centreville) interchange. West of that, the eastbound I-66 corridor operates under free-flow conditions.



Figure 9.4: I-66 Corridor – Existing Conditions PM Peak Period Densities (veh/ml/ln)



Figure 9.4b: I-66 Corridor – Existing Conditions PM Peak Period Densities (veh/ml/ln)



Figure 9.4c: I-66 Corridor – Existing Conditions PM Peak Period Densities (veh/ml/ln)



Figure 9.4d: I-66 Corridor – Existing Conditions PM Peak Period Densities (veh/ml/ln)



Existing PM Travel Time

Figure 9.5 shows segment and cumulative corridor average travel times in the westbound direction during the PM peak period. The total time to traverse the entire corridor from the Dulles Toll Road to Old Tavern Road is 57 minutes and 41 minutes for general purpose and HOV traffic, respectively.

Figure 9.5: Existing PM Time Travel for I-66 Westbound

Existing PM Peak Intersection Operations In the PM system representative hour (4:30 p.m. to 5:30 p.m.), more intersections than those during the AM peak operate at failing conditions. Table 9.2 lists the intersections that operate at LOS E or worse during the PM system representative hour. As shown in Figure 9.6, approximately 25 percent of the intersections operate at LOS E or worse, of which 14 percent operate at LOS F. As with the AM peak, many of the study area intersections operate at adequate overall control LOS, but individual approaches may operate at failing conditions. See Appendix I of the Transportation Technical Report for approach intersection delay and LOS.



Table 9.2: Existing Conditions PM Intersections with LOS E or LOS F (4:30 – 5:30 p.m.)

Figure Intersection


Intersection Delay

(Sec/veh) LOS

8 US 15/Route 55/Washington Street 59.1 E

9 US 29 Ramps/Linton Hall Road 88.2 F

11 US 29/I-66 WB Ramps/Heathcote Blvd 64.1 E



21 US 29/Stone Rd 101.7 F

26 Route 28/Ellanor C. Lawrence Park 179.8 F

27 Route 28/Braddock Rd/Walney Rd 75.3 E

30 Route 645/Fair Lakes Blvd 118.2 F

42 US 50/Waples Mill Road 124.9 F

43 US 50/Jermantown Road 151.5 F

44 Route 123/Jermantown Road 103.5 F

46 Route 123/Eaton Pl/Oak Pl 70.6 E

47 Route 123/Fairfax Blvd (Route 50/US 29) 109.8 F

56 Route 243/US 29 80.4 F

57 Route 7/Idylwood Road 65.0 E

64 US 29/Route 28 SB On-Ramp/Newgate Shopping Center Entrance 60.8 E

66 US 29/Old Centreville Road/Braddock Road 73.1 E

73 West Ox Road/US 29 Off-Ramp 189.3 F

80 Gallows Road/I-495 SB Off-Ramp/Woodburn Road 198.9 F

84 Westfields Boulevard/Stonecroft Boulevard 117.6 F * Intersection ID can be found in Appendix I of the TTR



Figure 9.6: Existing PM Representative Hour Intersection LOS Summary

9.2.2 2025 Conditions (No-Build vs. Phase 1)

2025 AM Peak Freeway Operations

2025 AM Travel Time Analysis

This section provides a brief overview of travel times in the 2025 No-Build and Phase I Alternative AM scenarios. Information is summarized for I-66 and Route 28 in both directions of travel.

Eastbound Direction Figure 9.7 shows a comparison of cumulative and incremental travel times along I-66 eastbound through the study area during the AM peak period. This figure provides a comparison between the 2025 Phase I, 2025 No-Build, and existing conditions. The figure differentiates between Express Lanes/HOV and general purpose lanes in each scenario.

Travel times in the 2025 Phase 1 conditions in the eastbound direction improve across all facility types as compared to travel times for the 2025 No-Build conditions. For general purpose traffic, average travel times for the entire mainline segment under the Phase 1 scenario are significantly shorter than those under the 2025 No-Build. There is a savings of more than 21 minutes overall as compared to the 2025 No-Build conditions and more than 20 minutes as compared to existing scenario. The travel time savings are most significant between Route 234 Bypass and US 50. This is generally the result from the proposed improvements at Route 28 and US 50 interchanges. Between US 50 and I-495, the travel times are similar in the Phase 1 scenario as compared to the No-Build. With the improvements at both Route 28 and US 50, traffic is no longer being metered at these locations and traffic is being released, causing the travel time benefit to be insignificant between US 50 and I-495.

Eastbound travel time savings for general purpose lanes among distinctive segments of the I-66 corridor are as follows:



Between US 15 and Route 234 Bypass, average general purpose travel times for Phase 1 are approximately 4 minutes during the AM representative hour. This represents a small savings of 0.5 minutes compared to the No-Build.

Between Route 234 Bypass and US 29 (Centreville), average general purpose travel times for Phase 1 are approximately 7.5 minutes during the AM representative hour. This represents a savings of approximately 15 minutes compared to the No-Build and a savings of approximately 18 minutes when compared to existing conditions.

Between US 29 (Centreville) and US 50, average general purpose travel times for Phase 1 are approximately 9.5 minutes during the AM representative hour. This represents a savings of about 7.5 minutes compared to the No-Build and a savings of approximately 4.5 minutes when compared to existing conditions.

Between US 50 and I-495, average general purpose travel times for Phase 1 are approximately 12 minutes, which are not much different from those of the No-Build and existing conditions during the AM representative hour.

General purpose lane travel time reductions in the eastbound (peak) direction along the corridor can be attributed to several factors:

The separation of high-occupancy vehicle (HOV) traffic from general purpose traffic with flexible-post bollards in the Phase 1 scenario starting at US 29 (Gainesville), which eliminates the weave between general purpose and concurrent HOV facilities that is otherwise possible under No-Build conditions.

The additional general purpose auxiliary lane between interchanges east of US 29 (Centreville) in the Phase 1, which increases the capacity and provides congestion relief for the general purpose facilities.

The removal of traffic signals on Route 28, particularly those along Route 28 northbound, which cause queue spillback onto I-66 in both directions under No-Build conditions. The addition of a general purpose to Express Lanes slip ramp west of Route 28 interchange provides extra capacity and access for traffic to maneuver over the highly-congested section of general purpose lanes.

The reconfiguration of several interchanges and arterial intersections, which reduces queue spillback onto ramps and the I-66 mainline.

The attraction of demand to use the tolled Express Lanes facility, which, as a two-lane, bollard-separated facility, has a much higher capacity and greater threshold speed that is regulated than the HOV lane under No-Build conditions.

Significant improvement can also be seen when comparing travel times for Express Lanes of 2025 Phase 1 scenario with those of the HOV lanes in the 2025 No-Build scenario:

For the entire I-66 Express Lanes facility, between US 15 and I-495, average Express Lanes travel times for Phase 1 are approximately 22.9 minutes during the representative hour, which represents a savings of roughly 8 minutes when compared to the HOV-3+ lane under No-Build conditions and about 10 minutes when compared to the HOV-2+ lane under existing conditions. When compared to general purpose lanes travel times, this represents a savings of approximately 31.5 minutes compared to No-Build conditions and approximately 31 minutes compared to existing conditions.

Eastbound AM Express Lanes travel time reductions along the corridor can be attributed to several factors:



The separation of HOV traffic from general purpose traffic with flexible-post bollards in Build scenarios, which removes the ability to weave between general purpose and the concurrent HOV lanes as is possible under existing and No-Build conditions.

The increased capacity of the Express Lanes facility due to the bollard separation, second through lane, and 65 mph speed limit.

The No-Build conditions HOV travel times do not account for the additional delay that can be expected due to friction and increase in violators due to increased general purpose delays. Hence the travel time benefits may actually be greater than what are being reported through the microsimulation.

The improved access from the Express Lanes to adjacent interchanges along the corridor as opposed to HOV traffic weaving to get to and from the general purpose ramps.



Figure 9.7: 2025 Phase 1 Alternative, No-Build, and Existing AM Travel Time comparison for I-66 Eastbound

0

10

20

30

40

50

60

70

I-66 EB: OldTavern Road

to US 15

I-66 EB: US15 to US 29(Gainesville)

I-66 EB: US29

(Gainesville)to Route 234

Bypass

I-66 EB:Route 234Bypass toRoute 234Business

I-66 EB:Route 234Business to

US 29(Centreville)

I-66 EB: US29

(Centreville)to Route 28

I-66 EB:Route 28 to

FairfaxCounty

Parkway

I-66 EB:FairfaxCounty

Parkway toUS 50

I-66 EB: US50 to Route

123

I-66 EB:Route 123 toRoute 243

I-66 EB:Route 243 to

I-495

I-66 EB: I-495 to Route

7

Min

ute

s

Existing - General Purpose 2025 No-Build - General Purpose 2025 Phase I - General Purpose

Existing - HOV 2025 No-Build - HOV 2025 Phase I - Express Lanes

Existing Cumulative - General Purpose 2025 No-Build Cumulative - General Purpose 2025 Phase I Cumulative - General Purpose

Existing Cumulative - HOV 2025 No-Build Cumulative - HOV 2025 Phase I Cumulative - Express Lanes



Westbound Direction Figure 9.8 shows a comparison of cumulative and incremental travel of 2025 Phase 1, 2025 No-Build and existing scenarios for westbound I-66 during the AM peak period.

In the westbound direction, travel times for general purpose traffic during the peak period are similar between Phase 1 Alternative conditions and No-Build conditions. Overall, the average peak-period travel times along I-66 westbound general purpose lanes through the study area between I-495 and US 15 are approximately 27 minutes, which is similar in comparison to No-Build conditions. Average travel times along I-66 westbound through the study area along the Express Lanes facility are approximately 23.5 minutes, which represents a savings of 3.5 minutes in comparison to both No-Build conditions and existing conditions. The travel time savings from the Express Lanes can be attributed to the flow regulation to maintain a minimum speed threshold of 55 mph as opposed to the frictions on general purpose traffic lanes at many interchanges throughout the corridor.



Figure 9.8: 2025 Phase 1 Alternative, No-Build, and Existing AM Travel Time Comparison for I-66 Westbound



Route 28 During the AM period, travel times along Route 28 improve in the Phase 1 Alternative when compared to the No-Build in both the northbound and southbound directions. In the northbound direction, average travel times from US 29 to Westfields Boulevard are 3.5 minutes, which represents a savings of 0.5 minutes when compared to No-Build conditions. This reduction is attributable to a reduction in queues north of I-66 due to the removal of existing traffic signals (at both Braddock/Walney Road and E.C. Lawrence Park access) and improved ramp access to and from I-66. While some queuing still occurs in the northbound direction between Route 29 and I-66, particularly in the pre-peak period, the magnitude of these queues decreases upon entering the peak period. In the southbound direction, average travel times from Westfields Boulevard to US 29 are 3 minutes, which represents minimal savings (less than a minute) when compared to No-Build Conditions. This slight reduction is attributable to the removal of existing traffic signals and improved ramp access to and from I-66.

2025 AM Speed Analysis

Average speeds on general purpose lanes during the representative AM hour in the eastbound direction are at or near the posted speed limits at all points west of Monument Drive and east of Route 243. Moderate to congested speeds (in the range of 20 to 50 mph) are observed in several segments between US 50 and Route 243. The segment from Fairfax County Parkway to Route 123 showed speeds lower than 20 mph during the later portion of the AM peak period.

In the westbound direction, all general purpose segments are expected to operate at speeds greater than 50 mph.

Figure 9.9 depicts average speed contours on I-66 eastbound in 15-minute increments for existing, 2025 No-Build, and 2025 Phase 1. Traffic speeds improve in most of the freeway segments under the Phase 1 condition in comparison to the existing and No-Build along both the eastbound and westbound I-66 corridor. Figure 9.10 depicts a similar speed contour graphic for the westbound direction.

Along I-66 eastbound, the major bottleneck location in the 2025 No-Build is between US 15 and Route 28, which is completely eliminated in the 2025 Phase 1 scenario. The elimination of this bottleneck in the Phase 1 scenario can be attributed to: reduced demand in general purpose lanes due to the addition of Express Lanes and reconfiguration of the Route 28 interchange with I-66. 2025 No-Build speeds along this section range between 20 and 35 mph while Phase 1 speeds are greater than 55 mph. In No-Build, the second bottleneck location along I-66 eastbound is between Fairfax County Parkway and Route 123. In Phase 1, the speed contours show similar results with additional peak spreading into the early pre-peak hour. The third bottleneck between Route 123 and Route 243 has a higher impact on traffic speeds in the Phase 1 scenario when compared to No-Build. This is due to improved conditions upstream of this location in the Phase 1 scenario with allows a higher volume to reach the Route 123/Route 243 bottle neck, resulting in higher traffic density and slower travel speeds through this segment.

Along I-66 eastbound inside I-495, Figure 9.10 shows a reduction of speed during the early morning hours. This is the result of additional demand from users accessing the corridor from I-495 before the HOV restrictions are in place. It is important to note, that only for one single half-hour increment in the Phase 1 scenario, eastbound volumes are above capacity approaching the Dulles Toll Road merge, causing this congestion. In general, total volumes in the peak periods on the eastbound direction inside I-495 are forecasted to be slightly lower than No-Build in the Phase 1 scenario.

Along the Express Lanes in both directions, all segments operate at or near the posted speed limit.



Along Route 28, average speeds are at or near the posted speed limit in both the directions. Removal of traffic signals along the Route 28 corridor and geometric improvements at the I-66 and Route 28 interchange improve the flow of traffic.



Figure 9.9: 2025 Phase 1, No-Build and Existing AM Peak Period Speed Comparison for I-66 Eastbound General Purpose Lanes



Figure 9.10: 2025 Phase 1, No-Build and Existing AM Peak Period Speed Comparison for I-66 Westbound General Purpose Lanes



2025 AM Basic Freeway Segment Analysis

This section compares levels of congestion on basic freeway segments during the AM representative hour between the 2025 No-Build and 2025 Phase I Alternative scenarios.

Eastbound Direction Table 9.3 provides a list of basic freeway segments along I-66 eastbound in the 2025 No-Build AM representative hour that are congested (orange) or severely congested (red). Table 9.4 provides a list of basic freeway segments along I-66 eastbound (general purpose lanes) in the 2025 Phase I Alternative AM representative hour with similar levels of congestion. There are no congested basic freeway segments along the I-66 eastbound Express Lanes in the 2025 Phase I Alternative AM representative hour.

Table 9.3: Congested Basic Freeway Segments, 2025 No-Build AM – I-66 Eastbound

Location

No-Build AM

Average Speed (mph)

Average Density

(veh/mi/ln)

I-66 EB at Route 234 Bypass 35.3 57.3

I-66 EB east of Route 234 Bypass 26.6 59.6

I-66 EB west of Route 234 Business 25.6 83.3


I-66 EB east of Route 234 Business 27.1 62.5


I-66 EB at Rest Stop 33.1 64.0

I-66 EB east of Rest Stop 31.7 67.9

I-66 EB west of US 29 (Centreville) 30.7 66.8


I-66 EB east of US 29 (Centreville) 37.0 48.9

I-66 EB east of Stringfellow Rd HOV On-Ramp 37.6 39.1

I-66 EB east of Fairfax County Pkwy On-Ramp 26.5 67.4

I-66 EB between US 50 Off-Ramps 16.6 101.6

I-66 EB between US 50 Off-Ramp and On-Ramp 15.6 98.2

I-66 EB west of US 50 On-Ramp 26.1 74.4

Table 9.4: Congested Basic Freeway Segments, 2025 Phase 1 Alternative AM – I-66 Eastbound

Location

Phase 1 AM

Average Speed (mph)

Average Density

(veh/mi/ln)

I-66 EB at US 50 37.1 43.2

I-66 EB at Route 123 22.7 79.6



Westbound Direction In the 2025 No-Build scenario, no basic freeway segments along I-66 westbound are congested during the AM representative hour. In the Phase I Alternative scenario, no basic freeway segments along the I-66 westbound general purpose lanes or along the I-66 westbound Express Lanes are congested during the AM representative hour.

2025 AM Weaving Segment Analysis

This section compares levels of congestion on freeway weave segments during the AM representative hour in the 2025 No-Build and 2025 Phase I Alternative scenarios.

Eastbound Direction Table 9.5 and Table 9.6 provide a list of weave segments along I-66 eastbound that are congested (orange) and severely congested (red) during the AM representative hour for 2025 No-Build and the 2025 Phase I Alternative, respectively. It is noted that in the design of the Phase I Alternative general purpose lanes, new freeway weaving sections are present due to the auxiliary lane provided between interchanges east of US 29 (Centreville). The congestions result from the bottlenecks at Route 123 and Route 243. There are no congested freeway weave segments along the I-66 eastbound Express Lanes in the 2025 Phase I Alternative AM representative hour.

Table 9.5: Congested Weave Freeway Segments, 2025 No-Build AM – I-66 Eastbound

Table 9.6: Congested Weave Freeway Segments, 2025 Phase 1 Alternative AM – I-66 Eastbound

Location

Phase 1 AM

Average Speed (mph)

Average Density (veh/mi/ln)

I-66 EB between US 50 and Route 123 23.8 74.1

I-66 EB between Route 123 and Route 243 24.2 77.3

Westbound Direction In the 2025 No-Build scenario, no freeway weave segments along I-66 westbound are congested during the AM representative hour. In the Phase I Alternative scenario, no freeway weave segments along the I-66 westbound general purpose lanes or along the I-66 westbound Express Lanes are congested during the AM representative hour.

2025 AM Ramp Junction Segment Analysis

This section compares levels of congestion on freeway ramp junction (merge or diverge) segments during the AM representative hour in the 2025 No-Build and 2025 Phase I Alternative scenarios.

Location

No-Build AM

Average Speed (mph)


I-66 EB east of Monument Dr On-Ramp 19.7 73.6



Eastbound Direction Table 9.7 provides a list of freeway ramp junction segments along I-66 eastbound in the 2025 No-Build AM representative hour that are congested (orange) or severely congested (red). In the 2025 Phase I Alternative scenario, there are no congested ramp junction segments in the eastbound general purpose lanes or Express Lanes during the AM representative hour.

Table 9.7: Congested Ramp Junction Freeway Segments, 2025 No-Build AM – I-66 Eastbound

Location Link Type

No-Build AM

Average Speed (mph)


I-66 EB east of Route 234 Bypass Merge 30.8 52.7

I-66 EB west of Route 234 Business Diverge 23.3 80.2

I-66 EB east of Route 234 Business Merge 24.9 71.7

I-66 EB west of Rest Stop Diverge 34.7 55.3

I-66 EB east of Rest Stop Merge 31.5 62.0

I-66 EB west of US 29 (Centreville) Diverge 32.7 55.8

I-66 EB east of US 29 (Centreville) Merge 37.0 48.9

I-66 EB east of US 29 (Centreville) Diverge 37.0 48.9

I-66 EB east of Fairfax County Pkwy On-Ramp Merge 31.4 42.2

I-66 EB between US 50 Off-Ramps Diverge 15.2 105.2

I-66 EB west of US 50 On-Ramp Merge 20.6 74.5

I-66 EB west of Route 123 Diverge 26.9 70.7


Westbound Direction In the 2025 No-Build scenario, no ramp junction freeway segments along I-66 westbound are congested during the AM representative hour. In the Phase I Alternative scenario, no ramp junction freeway segments along the I-66 westbound general purpose lanes or along the I-66 westbound Express Lanes are congested during the AM representative hour.

2025 AM Overall Freeway Density Results

Compared to the 2025 No-Build scenario, the Phase I Alternative is expected to operate with fewer areas of congestion in the eastbound direction along the I-66 corridor during the AM representative hour. Figure 9.11 provides a graphical comparison of the No-Build and Phase I Alternative basic freeway, weave, and ramp junction segment densities during the AM representative hour. In the No-Build scenario, a total of 30 segments are expected to operate in congested or severely congested conditions. In the Phase I Alternative, only 4 segments are expected to operate under similar conditions. Although there are 13 fewer segments considered in the Phase I Alternative due to geometric enhancements, the percentage of congested segments drops from 42 percent in the No-Build scenario to just 7 percent in the Phase I Alternative.

Figure 9.12 (a, b, c, and d) provides a geographic summary of vehicle densities along the I-66 corridor in the AM representative hour for the general purpose lanes in the No-Build and Phase I Alternative scenarios as well as the Express Lanes in the Phase I Alternative. The summary is presented both eastbound and westbound directions.



Figure 9.11: Summary of 2025 AM Representative Hour Segment Densities

No-Build (left) and Phase 1 Alternative (right)



Figure 9.12: 2025 AM Representative Hour Summary of Vehicle Densities



Figure 9.12b: 2025 AM Representative Hour Summary of Vehicle Densities



Figure 9.12c: 2025 AM Representative Hour Summary of Vehicle Densities



Figure 9.12d: 2025 AM Representative Hour Summary of Vehicle Densities



2025 AM Ramp Queues

This section compares queuing on freeway ramps during the AM peak and shoulder hours between the 2025 No-Build and 2025 Phase I Alternative scenarios. Both the No-Build and Phase 1 scenario are expected to contain several locations in which the average queue length exceeds the available storage.

Table 9.8 contains a list of ramps where average queues exceed available storage in the AM peak and shoulder hours under No-Build and or Phase 1 conditions. Queues which surpass available storage result in backups onto the mainline of I-66 or adjacent arterials. Under No-build conditions, average queues on the I-66 westbound on-ramp from northbound Fairfax County Parkway exceed the storage of the loop ramp and eventually congest the weave area and spill back onto the eastbound C-D road and mainline of I-66 in the shoulder period. This significant queuing issue was mitigated in Phase 1. However, the I-66 eastbound on-ramp from US 50 eastbound sees average queue lengths exceed the available storage length and back onto US 50 eastbound. This can be attributed to the higher demand using that ramp as well as higher through volumes on I-66 eastbound general purpose lanes. The Phase 1 scenario carries approximately 50 percent more traffic than the No-Build scenario. Improvements at the Route 28 interchange increase the throughput as compared to the No-Build scenario; however, capacity limitation at Route 123 result in a bottleneck at this interchange, affecting operations at the US 50 on-ramp. The anticipated queue is expected to be maintained within the free flow lanes of US 50. It is important to note that the on-ramp volume is higher in Phase 1 than the Preferred Alternative and is approaching the available capacity. Mitigation of the anticipated queuing would require capacity improvements to the general purpose lanes of I-66 eastbound through the Nutley Street interchange, requiring substantial right-of-way. The magnitude of queuing that can be expected along US 50 eastbound is comparable to existing conditions today; therefore, no mitigation is recommended at this location as part of this project. A complete table of queues on all ramps in the study area in the 2040 No-Build scenario can be found in Appendix J of the Transportation Technical Report.

Table 9.8: 2025 AM Ramps Where Average Queues Exceed Available Storage

Comparison of No-Build and Phase 1 Alternative

Ramp Location

2025 No-Build 2025 Phase 1 Alternative

Average Queue (feet)

95th Percentile

Queue (feet)

Available Storage

(feet)


95th Percentile

Queue (feet)

Available Storage

(feet)

I-66 WB On-Ramp from Fairfax County

Parkway NB 1,621 5,321 1,309 0 0 1,309

I-66 EB On-Ramp from US 50 EB

46 285 1,825 2,233 5,069 1,825

2025 AM Peak Intersection Operations

2025 AM Intersection Delay and Level of Service

This section describes the intersection and arterial performances in the study area during the AM representative hour for the 2025 Phase 1 Alternative. Table 9.9 provides a list of intersections with level of service E or worse during the AM representative hour. A complete list of intersections in the study area along with LOS for the AM representative hour, as well as LOS for each intersection’s worst hour during the AM peak and shoulder period, can be found in Appendix I of the Transportation Technical Report.



Table 9.9: 2025 No-Build and Phase 1 Alternative AM Intersections with LOS E or F (7:00 – 8:00 a.m.)

Figure Intersection


No Build Phase 1

Intersection Delay

(Sec/veh) LOS

Intersection Delay

(Sec/veh) LOS

8 US 15/Route 55/Washington St 26.9 C 85.0 F

14 University Blvd/Wellington Rd 31.9 C 66.8 E

89 University Blvd/I-66 Express Lanes Ramps - - 167.1 F

20 Route 234 Business/Balls Ford Rd 99.8 F 83.4 F

21 US 29 (Centreville)/Stone Rd 56.0 E 52.8 D

42 US 50/Waples Mill Rd 68.0 E 88.1 F

44 Route 123/Jermantown Rd 88.8 F 111.7 F

45 Route 123/Rose Forest Dr/White Granite Rd 37.1 D 62.8 E

99 Route 243/I-66 EB Ramps - - 86.7 F

57 Route 7/Idylwood Rd 79.5 E 82.4 F

62 Route 7/Haycock Rd/Shreve Rd 57.3 E 52.7 D

80 Gallows Rd/I-495 SB Off-Ramp/Woodburn Rd 49.5 D 57.5 E

82 Gallows Rd/I-495 NB Ramps 90.2 F 130.1 F

Figures 9.13 and 9.14 provides pie charts summarizing overall intersection LOS and individual intersection approach LOS for the AM representative hour for the 2025 No-Build and 2025 Phase 1 Alternative scenarios. Overall, 11 percent of intersections during the 2025 Phase 1 Alternative scenario operate at LOS E or worse during the AM representative hour, compared to 8 percent under No-Build conditions. The percent of approaches that operate at LOS E or worse during the AM peak hour is 18 percent in the 2025 Phase 1 Alternative in comparison to 15 percent under No-Build conditions. In some locations, this reduction in arterial performance can be attributed to an increase in arterial volume due to new access to the I-66 Express Lanes facility, such as along Route 123. In other locations, the Phase 1 Alternative may artificially appear to perform worse during the AM representative hour in comparison to the No-Build scenario if more demand is being constrained upstream in the No-Build scenario due to congestion.



Figure 9.13: 2025 No-Build AM Representative Hour Intersection LOS Summary

Figure 9.14: 2025 Phase 1 Alternative AM Representative Hour Intersection LOS Summary

2025 AM Intersection Queues

This section briefly describes intersection queuing in the study area and provides a comparison of intersection performance during the AM peak and shoulder period between the 2025 No-Build and 2025 Phase 1 Alternative scenarios. Mitigating queue spillback requires a balance between accommodating 95th percentile queue lengths within the storage lane, optimization of green time at traffic signals, and minimizing construction impacts to adjacent properties to accommodate the projected vehicle queues. Queue spillback of 10 vehicles (or 250 feet) beyond the available storage capacity of a particular movement based upon the average queue length was identified as the threshold for which consideration



of geometric modifications might be warranted. This indicates a significant recurring pattern of queue spillback that could impact the safety and operations of adjacent movements.

In the No-Build scenario, a total of 30 movements exceed the available storage provided. Of these movements, 7 are expected to have an average queue length that extends 250 feet or more beyond the available storage capacity. In the Phase 1 Alternative, a total of 33 movements exceed the available storage, of which a total of 7 movements are expected to have an average queue length that extends 250 feet or more beyond the available storage capacity. A complete list of queuing at all intersection approaches in the study area can be found in Appendix I of the Transportation Technical Report. A summary of arterial intersection minor improvements and other potential mitigation measures can be found in Sections 9.2.4 and 9.2.5 of this report.

2025 AM Intersection Considerations

A detailed description of arterial intersection minor improvements and other potential mitigation measures can be found in Sections 9.2.4 and 9.2.5 of this report. The mitigation measures provided encompass the intersection locations where LOS F is expected and queuing degradation occurs in the Build alternative but not in the No-Build scenario. If excessive delay (LOS E or worse) and queuing is expected in both scenarios beyond the 250-foot threshold, specific mitigation is not recommended. Based on the findings of the Phase 1 AM analyses, specific mitigation measures are not recommended; however, monitoring of operations and consideration of future detailed analyses of the US 15 and Route 55/Washington Street intersection should be considered.

2025 PM Peak Freeway Operations

2025 PM Travel Time Analysis

This section provides a brief overview of travel times in the 2025 No-Build and Phase I Alternative scenarios. Information is summarized for I-66 and Route 28 in both directions of travel.

Westbound Direction 2025 Phase 1 travel times in the westbound direction improve for all facility types when compared to the 2025 No-Build scenario. For general purpose traffic, travel time improvements are seen for all segments between I-495 and Route 234 Bypass, with significant travel time savings between I-495 and US 29 (Centreville). General westbound travel time savings among distinctive segments of the I-66 corridor are as follows:

Between I-495 and Route 243 (Nutley Street), average general purpose travel times for Phase 1 are approximately 3.5 minutes during the PM peak period. This represents a savings of approximately 8 minutes compared to the No-Build scenario and 6 minutes compared to existing conditions.

Between Route 243 (Nutley Street) and US 50, average general purpose travel times for the Phase 1 are approximately 4.5 minutes during the PM peak period. This represents a savings of approximately 8 minutes compared to No-Build and existing conditions.

Between US 50 and US 29 (Centreville), average general purpose travel times for the Phase 1 are approximately 6.5 minutes during the PM peak period. This represents a savings of approximately 4.5 minutes compared to the No-Build scenario and 5 minutes compared to existing conditions.

Between US 29 (Centreville) and Route 234 Business, average general purpose travel times for the Phase I are approximately 5 minutes during the PM peak period. This represents a savings of



approximately 1.5 minutes compared to the No-Build scenario and 2.5 minutes compared to existing conditions.

Between Route 234 Business and US 15, the average general purpose travel times during the PM peak period do not change significantly from the No-Build scenario.

The average general purpose travel time between I-495 and US 15 in the PM peak period is approximately 26 minutes. This represents a savings of approximately 18 minutes when compared to No-Build conditions and 17 minutes when compared to existing conditions.

Reductions in general purpose lane travel times, especially between I-495 and US 29 (Centreville), can be attributed to several factors:

The additional general purpose auxiliary lane between interchanges east of US 29 (Centreville) in the Phase 1, which increases the capacity of the general purpose facilities in comparison to the No-Build configuration.

The separation of HOV traffic from general purpose traffic with flexible-post bollards in the Phase 1, which removes the ability to weave between general purpose lanes and HOV lane(s), which reduces speeds on both facilities in the No-Build conditions.

The removal of traffic signals on Route 28, particularly those along Route 28 northbound, which see queues spilling back onto I-66 in both directions under No-Build conditions.

The shift in some general purpose demand to use the Express Lanes facility, which, as a two-lane bollard-separated facility, has a much higher capacity than the HOV lane under No-Build conditions.

The redesigned interchanges and improvements for adjacent arterial intersections along the corridor provide more capacity to the exiting traffic from I-66 and reduce the queue spillover to the freeway.

Average travel times in the westbound direction are also shorter in the Phase 1 Express Lanes when compared to the HOV lanes under existing and 2025 No-Build scenarios for all segments between I-495 and US 15:

Between I-495 and US 29 (Centreville), average Express Lanes travel times for the Phase 1 are approximately 12 minutes during the representative hour, which represents a savings of approximately 5.5 minutes when compared to the HOV-3+ lanes under No-Build conditions and approximately 7.5 minutes when compared to the HOV-2 lanes under existing conditions. When compared to general purpose traffic, this represents a savings of approximately 23 minutes compared to the general purpose lanes under No-Build conditions and approximately 20.5 minutes compared to the general purpose lanes under existing conditions.

HOV/Express Lanes travel time reductions along the length of the corridor in the westbound direction can be attributed to several factors:

The separation of HOV traffic from general purpose traffic with flexible-post bollards in Phase 1, which removes the ability to weave between general purpose lanes and the HOV lane. This weaving reduces speeds on both facilities in the No-Build conditions.

The increased capacity of the Express Lanes facility due to the flexible-post bollard separation, second through lane, and 65 mph posted speed limit.

Cumulative and incremental westbound travel times between each interchange are shown in Figure 9.15 for the PM peak period along the I-66 corridor, the figure differentiates between Express Lane/HOV traffic and general purpose traffic in each scenario.



Figure 9.15: 2025 Phase 1 Alternative, No-Build and Existing PM Travel Time Comparison for I-66 Westbound



Eastbound Direction In the eastbound direction, travel times between US 15 and US 50 remain relatively unchanged between the 2025 Phase 1 Alternative, 2025 No-Build, and existing conditions scenarios. East of US 50, the 2025 Phase 1 Alternative sees slightly higher travel times due to occasional queue spillback from the ramp to I-495 southbound. In 2025, capacity improvements on I-495 southbound upstream of I-66 allow more volume to travel south toward its interchange with US 50. In the 2025 Phase 1 Alternative simulations, the weave area on I-495 southbound between I-66 and US 50 would occasionally cause queues to spill back onto I-66 eastbound, resulting in slower speeds. At the same time, should these queues form in the field, drivers heading eastbound on I-66 under the Phase 1 Alternative will have the option to use the I-66 Express Lanes to access the I-495 southbound Express Lanes and avoid any backups on I-66 eastbound and I-495 southbound. They could choose to access the I-66 eastbound Express Lanes at the flyover from the eastbound general purpose lanes just west of I-495 or points further upstream. Travel times on I-66 eastbound Express Lanes are lower than travel times in the general purpose lanes in the Phase 1 Alternative, No-Build, and existing conditions due to the posted 65 mph speed limit.

Figure 9.16 gives a comparison of cumulative and incremental eastbound travel times for existing, No-Build, and Phase 1 Alternative scenarios along the I-66 study area during the PM peak period.



Figure 9.16: 2025 Phase 1 Alternative, No-Build and Existing PM Travel Time Summary for I-66 Eastbound



Route 28 Travel times along Route 28 improve in both the northbound and southbound directions in the Phase 1 scenario when compared to 2025 No-Build conditions. In the northbound direction, average travel times from US 29 to Westfields Boulevard are approximately 3 minutes, which represents a savings of 1 minute when compared to No-Build conditions. In the southbound direction, average travel times from Westfields Boulevard to US 29 are approximately 4 minutes, which represents a savings of 4 minutes when compared to No-Build conditions. This reduction is attributable to the removal of existing traffic signals and improved ramp access to and from I-66.

2025 PM Speed Analysis

In the PM peak period, it can be observed from the exhibits that speeds remain at or near free-flow speeds throughout most of the corridor under the Phase 1 scenario. The three major sources of congestion in the existing and No-Build models are: the Route 123 interchange, the Route 28 and US 29 interchanges, and the interchange at Route 234 Bypass. Through improved interchange geometry, augmented by the displacement of traffic volume to the bollard-separated Express Lanes, these locations have no appreciable effect on vehicle speeds under the Phase 1 scenario.

Figure 9.17 illustrates the PM peak period 15-minute average speeds along I-66 westbound in 15-minute increments for existing, 2025 No-Build, and 2025 Phase 1 Alternative conditions. Traffic speeds improve under the Phase 1 condition in comparison to the existing and No-Build conditions along both the eastbound and westbound I-66 corridor. Figure 9.18 depicts a similar speed contour graphic for the eastbound direction.



Figure 9.17: 2025 Phase 1, No-Build and Existing PM Peak Period Speed Comparison for I-66 Westbound General Purpose Lanes



Figure 9.18: 2025 Phase 1, No-Build and Existing PM Peak Period Speed Comparison for I-66 Eastbound General Purpose Lanes



2025 PM Basic Freeway Segment Analysis

This section compares levels of congestion on basic freeway segments during the PM representative hour between the 2025 No-Build and 2025 Phase I Alternative scenarios.

Westbound Direction Table 9.10 provides a list of basic freeway segments along I-66 westbound in the 2025 No-Build PM representative hour that are congested (orange) or severely congested (red). There are no congested basic freeway segments along the I-66 westbound general purpose lanes and Express Lanes in the 2025 Phase I Alternative PM representative hour.

Table 9.10: Congested Basic Freeway Segments, 2025 No-Build PM – I-66 Westbound

Location

No-Build PM Average Speed (mph)

Average Density

(veh/mi/ln)

I-66 WB west of I-495 30.7 46.3

I-66 WB west of I-495 32.5 60.6

I-66 WB west of I-495 29.2 68.5

I-66 WB east of Route 243 20.9 97.7

I-66 WB west of Route 243 21.9 91.0

I-66 WB west of Vaden Dr On-Ramp 17.1 101.7


I-66 WB between Fairfax County Pkwy Off-Ramp and On-Ramp 42.7 41.6

I-66 WB west of Stringfellow Rd Off-Ramp 19.3 78.6

I-66 WB east of US 29 (Centreville) 37.0 47.3

I-66 WB at Rest Stop 36.8 58.6

Eastbound Direction Table 9.11 provides a list of basic freeway segments along I-66 eastbound in the 2025 No-Build PM representative hour that are congested (orange) or severely congested (red). In the Phase I Alternative scenario, no basic freeway segments along the I-66 eastbound general purpose lanes or Express Lanes are congested during the PM representative hour.

Table 9.11: Congested Basic Freeway Segments, 2025 No-Build PM – I-66 Eastbound

Location No-Build PM

Average Speed (mph)


I-66 EB east of Dulles Toll Rd 7.1 105.9

2025 PM Weaving Segment Analysis

This section compares levels of congestion on freeway weave segments during the PM representative hour in the 2025 No-Build and 2025 Phase I Alternative scenarios.



Westbound Direction Table 9.12 provides a list of weave segments along I-66 westbound that are congested (orange) and severely congested (red) during the 2025 No-Build PM representative hour scenario. In the Phase I Alternative scenario, no freeway weave segments along the I-66 westbound general purpose lanes or along the I-66 westbound Express Lanes are congested during the PM representative hour.

Table 9.12: Congested Weave Freeway Segments, 2025 No-Build PM – I-66 Westbound

Location No-Build PM

Average Speed (mph)


I-66 WB west of Route 28 On-Ramp 40.8 38.5

Eastbound Direction In the 2025 No-Build scenario, no basic freeway segments along I-66 eastbound are congested during the PM representative hour. In the Phase I Alternative scenario, no basic freeway segments along the I-66 eastbound general purpose lanes or along the I-66 eastbound Express Lanes are congested during the PM representative hour.

2025 PM Ramp Junction Segment Analysis

This section compares levels of congestion on freeway ramp junction (merge or diverge) segments during the PM representative hour in the 2025 No-Build and 2025 Phase I Alternative scenarios.

Westbound Direction Table 9.13 provides a list of freeway ramp junction segments along I-66 westbound in the 2025 No-Build PM representative hour that are congested (orange) or severely congested (red). There are no congested freeway ramp junction segments along I-66 westbound (general purpose lanes and Express Lanes) in the 2025 Phase I Alternative during the PM representative hour.

Table 9.13: Congested Ramp Junction Freeway Segments, 2025 No-Build PM – I-66 Westbound

Location Link Type

No-Build PM

Average Speed (mph)


I-66 WB at I-495 Merge 34.4 35.2

I-66 WB west of I-495 SB Express Lanes Ramp Merge 36.2 40.8

I-66 WB west of I-495 Merge 33.5 44.9

I-66 WB west of I-495 NB Express Lanes Ramp Merge 28.8 48.3

I-66 WB east of Route 243 Diverge 26.3 77.6

I-66 WB west of Route 243 Merge 22.7 80.2

I-66 WB west of Vaden Dr On-Ramp Merge 12.2 103.7






Location Link Type

No-Build PM

Average Speed (mph)


I-66 WB east of Stringfellow Rd Off-Ramp Diverge 29.9 53.5

I-66 WB west of Fairfax County Pkwy On-Ramp Merge 35.8 48.7

I-66 WB at US 29 (Centreville) Merge 33.8 50.2

I-66 WB west of US 29 (Centreville) Merge 39.6 43.3

I-66 WB east of Rest Stop Diverge 38.8 50.8

Eastbound Direction Table 9.14 provides a list of freeway ramp junction segments along I-66 eastbound in the 2025 No-Build PM representative hour that are congested (orange) or severely congested (red). There are no congested freeway ramp junction segments along I-66 eastbound (general purpose lanes and Express Lanes) in the 2025 Phase I Alternative PM representative hour

Table 9.14: Congested Ramp Junction Freeway Segments, 2025 No-Build PM – I-66 Eastbound

Location Link Type

No-Build PM

Average Speed (mph)




I-66 EB east of Dulles Toll Rd Merge 6.7 102.7

2025 PM Overall Freeway Density Results

Compared to the 2025 No-Build scenario, the Phase I Alternative is expected to operate with fewer areas of congestion in the westbound direction along the I-66 corridor during the PM representative hour. Figure 9.19 provides a graphical comparison of the No-Build and Phase I Alternative basic freeway, weave, and ramp junction segment densities for the westbound direction during the PM representative hour. In the No-Build scenario, a total 31 segments are expected to operate in congested or severely congested conditions. In the Phase I Alternative, only 1 segment is expected to operate under similar conditions. Although there are 14 fewer segments considered in the Phase I Alternative due to geometric enhancements, the percentage of congested segments drops from 34 percent in the No-Build scenario to almost no congested segments in the Phase I Alternative.

Figure 9.20 (a, b, c, and d) provides a geographic summary of vehicle densities along the I-66 corridor in the PM representative hour for the general purpose lanes in the No-Build and Phase I Alternative scenarios as well as the Express Lanes in the Phase I Alternative. The summary is presented for both eastbound and westbound directions.



Figure 9.19: Summary of 2025 PM Representative Hour Segment Densities

No-Build (left) and Phase 1 Alternative (right)



Figure 9.20: 2025 PM Representative Hour Summary of Vehicle Densities



Figure 9.20b: 2025 PM Representative Hour Summary of Vehicle Densities



Figure 9.20c: 2025 PM Representative Hour Summary of Vehicle Densities



Figure 9.20d: 2025 PM Representative Hour Summary of Vehicle Densities



2025 PM Ramp Queues

This section compares queuing on freeway ramps during the PM peak and shoulder period between the 2025 No-Build and 2025 Phase I Alternative scenarios. The No-Build scenario contains several locations in which the average queue length exceeds the available storage; the Phase I Alternative scenario has one location in which the average queue length exceeds available storage for all the ramps. All instances of average queues extending beyond available storage in either scenario during the PM peak and shoulder period occur on I-495.

Table 9.15 contains a list of ramps where average queues exceed available storage in the PM peak and shoulder period under No-Build and or Phase 1 conditions. During these PM time periods, queues exceed available storage at interchange locations on I-495. Congestion at merge locations results in C-D road and ramp queues reaching eastbound Route 7 along with eastbound and westbound US 50, as indicated below. Since these locations are outside of the IJR study area, no mitigation measures are recommended at these locations. A complete table of queues on all ramp in the study area in the 2025 No-Build scenario can be found in Appendix J of the Transportation Technical Report.

Table 9.15: 2025 PM Ramps Where Average Queues Exceed Available Storage

Comparison of No-Build and Phase 1 Alternative

Ramp Location

2025 No-Build 2025 Phase 1 Alternative


95th Percentile

Queue (feet)

Available Storage

(feet)


95th Percentile

Queue (feet)

Available Storage

(feet)

I-495 SB On-Ramp from C-D Road at Route 7

2,900 5,313 1,453 0 0 1,453

I-495 NB On-Ramp from US 50 WB to NB C-D Road

1,231 5,264 725 3,039 5,328 725

I-495 SB On-Ramp from C-D Road at US 50 WB

2,054 5,306 918 847 5,301 918

I-495 SB On-Ramp from US 50 EB to SB C-D Road

3,162 4,776 1,600 26 192 1,600

2025 PM Peak Intersection Operations

2025 PM Intersection Delay and Level of Service

This section describes the intersection and arterial performances in the study area during the PM representative hour for the 2025 No-Build and Phase 1 Alternative. Table 9.16 provides a list of intersections with level of service E or worse during the PM representative hour. A complete list of intersections in the study area along with LOS for the PM representative hour, as well as LOS for each intersection’s worst hour during the PM peak and shoulder period, can be found in Appendix I of the Transportation Technical Report.



Table 9.16: 2025 No-Build and Phase 1 Alternative PM Intersections with LOS E or F (4:30 – 5:30 p.m.)

Figure Intersection


No Build Phase 1

Intersection Delay

(Sec/veh) LOS

Intersection Delay

(Sec/veh) LOS

12 US 29 (Gainesville)/University Blvd 43.2 D 70.1 E

14 University Blvd/Wellington Rd 52.2 D 60.3 E

20 Route 234 Business/Balls Ford Rd 62.5 E 65.0 E

21 US 29 (Centreville)/Stone Rd 114.0 F 117.9 F

24 US 29 (Centreville)/I-66 EB Ramps 77.4 E 69.0 E

64 US 29 (Centreville)/Route 28 SB On-Ramp/ Newgate Shopping Center Entrance

92.2 F 28.9 C

66 US 29 (Centreville)/Old Centreville Rd/Braddock Rd 130.1 F 69.0 E

83 Westfields Blvd/Park Meadow Dr/Newbrook Dr 36.0 D 109.8 F

84 Westfields Blvd/Stonecroft Blvd 76.3 E 57.0 E

26 Route 28/Ellanor C. Lawrence Park 128.2 F - -

27 Route 28/Braddock Rd/Walney Rd 76.6 E 64.5 E

30 Stringfellow Rd/Fair Lakes Blvd 70.0 E 57.9 E

38 Monument Dr/I-66 Express Lanes Ramps 8.0 A 106.2 F

39 Monument Dr/Government Center Pkwy 23.1 C 94.1 F

42 US 50/Waples Mill Rd 154.3 F 144.0 F

43 US 50/Jermantown Rd 107.5 F 107.6 F


46 Route 123/Eaton Pl/Oak Pl 8.0 A 145.1 F

47 Route 123/US 50/US 29 75.0 E 74.9 E

54 Route 243/Saintsbury Dr/Swanee Ln 28.9 C 77.8 E

56 Route 243/US 29 109.1 F 130.9 F

99 Route 243/I-66 EB Ramps - - 113.7 F

98 Route 243/I-66 WB Ramps - - 59.5 E

57 Route 7/Idylwood Rd 148.1 F 142.1 F

62 Route 7/Haycock Rd/Shreve Rd 57.0 E 63.4 E

78 Route 7/I-495 Express Lanes Ramps/ I-495 NB On-Ramp

156.9 F 16.7 B

80 Gallows Rd/I-495 SB Off-Ramp/Woodburn Rd 66.3 E 75.1 E

Figures 9.21 and 9.22 provides pie charts summarizing overall intersection LOS and individual intersection approach LOS for the PM representative hour for the 2025 Phase 1 Alternative scenario. Overall, 24 percent of intersections during the 2025 Phase 1 Alternative scenario operate at LOS E or worse during the PM representative hour, compared to 20 percent under No-Build conditions. The percent of approaches that operate at LOS E or worse during the PM representative hour is 26 percent in the 2025 Phase 1 Alternative in comparison to 25 percent under No-Build conditions. In some locations, this reduction in arterial performance can be attributed to an increase in arterial volume due to new access to the I-66 Express Lanes facility, such as along Route 123. In other locations, the Phase 1 Alternative may artificially appear to perform worse during the PM representative hour in comparison to



the No-Build scenario if more demand is being constrained upstream in the No-Build scenario due to congestion.

Figure 9.21: 2025 No-Build PM Representative Hour Intersection LOS Summary

Figure 9.22: 2025 Phase 1 PM Representative Hour Intersection LOS Summary

2025 PM Intersection Queues

This section briefly describes intersection queuing in the study area and provides a comparison of intersection performance during the PM representative hour between the 2025 No-Build and 2025 Phase 1 Alternative scenarios. Mitigating queue spillback requires a balance between accommodating 95th



percentile queue lengths within the storage lane, optimization of green time at traffic signals, and minimizing construction impacts to adjacent properties to accommodate the projected vehicle queues. Queue spillback of 10 vehicles (or 250 feet) beyond the available storage capacity of a particular movement based upon the average queue length was identified as the threshold for which consideration of geometric modifications might be warranted. This indicates a significant recurring pattern of queue spillback that could impact the safety and operations of adjacent movements.

In the No-Build scenario, a total of 50 movements exceed the available storage provided. Of these movements, 22 are expected to have an average queue length that extends 250 feet or more beyond the available storage capacity. In the Phase 1 Alternative, a total of 56 movements exceed the available storage, of which a total of 18 movements are expected to have an average queue length that extends 250 feet or more beyond the available storage capacity. A complete list of queuing at all intersection approaches in the study area can be found Appendix I of the Transportation Technical Report. A summary of arterial intersection minor improvements and other potential mitigation measures can be found in Sections 9.2.4 and 9.2.5 of this report.

2025 PM Intersection Considerations

A detailed description of arterial intersection minor improvements and other potential mitigation measures can be found in Sections 9.2.4 and 9.2.5 of this report. The mitigation measures provided encompass the intersection locations where LOS F is expected and queuing degradation occurs in the Build alternative but not in the No-Build scenario. If excessive delay (LOS E or worse) and queuing is expected in both scenarios beyond the 250-foot threshold, specific mitigation is not recommended. The following summarize the potential mitigation measures outlined in Sections 9.2.4 and 9.2.5 that were identified based upon the findings of the 2025 PM Phase 1 analyses:

Westfields Boulevard/Park Meadow Drive – monitor operations and consider future detailed analyses, including the downstream interchange with Route 28.

Monument Drive/I-66 Express Lanes – provide exclusive eastbound left- and right-turn lanes from the off-ramp and reconfigure the southbound approach to provide exclusive lanes for the left, through, and right-turn movements (would reduce the northbound departure to two lanes).

Route 123/Eaton Place – reconfigure the westbound approach to provide dual right-turn lanes and a shared left and through lane (would reduce the eastbound departure to one lane).

9.2.3 2040 Conditions (No-Build vs. Preferred Alternative)

2040 AM Peak Freeway Operations

2040 AM Travel Time Analysis

This section provides a brief overview of travel times in the 2040 No-Build and Preferred Alternative scenarios. Information is summarized for I-66 and Route 28 in both directions of travel.

Eastbound Direction Travel times in the eastbound direction improve for general purpose traffic and Express Lanes/HOV traffic as compared to No-Build conditions. Cumulative travel time in the general purposes lanes is reduced from 82 minutes to 45.1 minutes between US 15 and Route 7. For general purpose traffic, average travel times in the eastbound direction are shorter than the 2040 No-Build scenario for all segments between US 15 and I-495 except for the segment between US 29 (Centreville) and US 50. The travel time savings are significant (37 minutes) between US 15 and US 29 (Centreville) during the AM peak in the Preferred



Alternative as compared to No-Build conditions. General purpose lane travel time reductions between US 15 and US 29 (Centreville) can be attributed to several factors:

The separation of HOV traffic from general purpose traffic with flexible-post bollards in the Preferred Alternative, which eliminates the weave between general purpose and concurrent HOV lanes (this is weave is possible under No-Build conditions).

The redesign of the Route 28/I-66 interchange: - Enhanced access is provided between I-66 and Route 28 by way of the general purpose

lanes and Express Lanes. - Traffic signals on Route 28 are removed, which cause queue spillback onto I-66 in both

directions under No-Build conditions. - The addition of a general purpose to Express Lanes slip ramp west of the Route 28

interchange provides extra capacity through the interchange and access for traffic to bypass the highly-congested section of the general purpose lanes.


The attraction of demand to use the tolled Express Lanes facility, which has a much higher capacity than the HOV lane under No-Build conditions.

The increase in travel time along the eastbound general purpose lanes between US 29 (Centreville) and US 50 can be attributed to the higher demand served by the improved Route 28/I-66 interchange in the Preferred Alternative than the No-Build as well as the geometric constraints at the Route 123 and Route 243 exit ramps. In addition, the total throughput of the I-66 corridor is greater in the Preferred Alternative than the No-Build condition.

For Express Lanes traffic, average travel times in the eastbound direction are shorter than the HOV segments in the 2040 No-Build scenario between US 15 and I-495. Express Lanes travel time reductions along the length of the corridor in the eastbound direction can be attributed to several factors:

The separation of HOV traffic from general purpose traffic with flexible-post bollards in the Preferred Alternative, which removes the ability to weave between general purpose and concurrent HOV lanes.

The increased capacity of the Express Lanes facility due to the bollard separation, second travel lane, and posted speed limit of 65 mph along the entire 25-mile corridor.

The HOV travel times in the No-Build condition do not account for additional delay that can be expected due to friction and increase in violators due to increased delays along the general purpose lanes; thus, the travel time benefits may actually be greater than what are being reported through the microsimulation.

The improved access from the Express Lanes to adjacent interchanges along the corridor, which is not provided for the current HOV lane configuration.

Figure 9.23 shows a comparison of cumulative and incremental travel times along I-66 eastbound through the study area during the AM peak period. This figure provides a comparison between the 2040 Preferred Alternative, 2040 No-Build, and existing conditions. The figure differentiates between Express Lanes/HOV and general purpose lanes in each scenario.



Figure 9.23: 2040 Preferred Alternative, 2040 No-Build, and Existing AM Travel Time Comparison – I-66 Eastbound



Westbound Direction In the westbound direction, travel times for general purpose traffic during the peak period are similar in the Preferred Alternative conditions when compared to 2040 No-Build conditions. Overall, the average peak period travel times along I-66 westbound general purpose lanes through the study area between I-495 and US 15 are approximately 25 minutes, which is similar to No-Build conditions. Average travel times along I-66 westbound through the study area along the Express Lanes facility are approximately 22 minutes, which represents a savings of 4 minutes in comparison to No-Build conditions. The travel time savings from the Express Lanes can be attributed to the elimination of friction caused by weaving patterns in the general purpose travel lanes at the interchanges between Route 243 and US 29 (Centreville).

Figure 9.24 shows a comparison of cumulative and incremental travel times along I-66 westbound through the study area during the AM peak period.



Figure 9.24: 2040 Preferred Alternative, 2040 No-Build, and Existing AM Travel Time Comparison – I-66 Westbound



Route 28 Travel times along Route 28, between US 29 (Centreville) and Westfields Boulevard, improve in both the northbound and southbound directions in the Preferred Alternative as compared to No-Build conditions. This reduction is attributable to a reduction in queues north of I-66 due to the removal of existing traffic signals and improved ramp access to and from I-66. While some queuing still occurs in the northbound direction from the on- and off-ramps to I-66 back to the ramps to and from US 29 (Centreville), the magnitude of these queues is diminished entering peak period, between 6:30 a.m. and 7:00 a.m.

2040 AM Speed Analysis

Average speeds on general purpose lanes during the AM peak period in the eastbound direction are at or near the posted speed limit up to Route 234 Business and east of Route 243. Moderate to congested speeds (in the range of 20 to 50 mph) are observed in several segments between Route 234 Business and Route 243. Consistent with the density levels, the segments from Route 28 to Route 123 showed speeds lower than 35 mph during the representative hour.

In the westbound (off peak) direction, all general purpose segments are expected to operate at speeds greater than 50 mph consistent with the density results, except for a spot location at US 50 interchange.

Figure 9.25 depicts average speed contours on I-66 eastbound in 15-minute increments for existing, 2040 No-Build, and 2040 Preferred Alternative general purpose lanes and Express Lanes. Traffic speeds along the general purpose lanes improve under the Preferred Alternative condition as compared to existing and No-Build conditions along the eastbound I-66 corridor. Figure 9.26 depicts a similar speed contour graphic for the westbound direction.

Along I-66 eastbound, the major bottleneck location in the 2040 No-Build is at Route 28 interchange, which is completely eliminated in the Preferred Alternative. As previously described, reconfiguration of the Route 28 and I-66 interchange significantly improves the flow of traffic. However, the improved traffic flow caused congestions at weaving sections between US 50 and Route 123 and between Route 123 and Route 243, with demand exceeding capacity at both locations. In comparison to No-Build where most of the segments between US 29 (Centreville) and Route 123 also operate under severely-congested speeds with less demand due to upstreaming constraint at Route 28, this is a significant improvement.

The bottleneck between Route 243 (Nutley Street) and I-495 in No-Build is minimized in the Preferred Alternative, and average speeds in this segment improve by more than 30 mph when compared to No-Build conditions. This can be attributed to the provision of an auxiliary lane and interchange configuration enhancements at I-495 that allows all movements between general purpose and Express Lanes of I-66 and I-495 using independent ramps.


Along Route 28, average speeds are at or near the posted speed limit in both the directions except for the slow-down that occurs in the pre-peak period for the northbound direction between US 29 and I-66. Removal of traffic signals along the Route 28 corridor and geometric improvements at I-66 and Route 28 interchange improve the flow of traffic.



Figure 9.25: 2040 Preferred Alternative AM Peak Period Speed Comparison – I-66 Eastbound General Purpose Lanes



Figure 9.26: 2040 Preferred Alternative AM Peak Period Speed Comparison – I-66 Westbound General Purpose Lanes

2040 AM Basic Freeway Segment Analysis

This section compares levels of congestion on basic freeway segments during the AM representative hour between the 2040 No-Build and 2040 Preferred Alternative scenarios.

Eastbound Direction Table 9.17 provides a list of basic freeway segments along I-66 eastbound in the 2040 No-Build AM representative hour that are congested (orange) or severely congested (red). Table 9.18 provides a list of freeway segments along I-66 eastbound (general purpose lanes) in the 2040 Preferred Alternative AM representative hour with similar levels of congestion.



Table 9.17: Congested Basic Freeway Segments, 2040 No-Build AM – I-66 Eastbound

Location No-Build AM

Average Speed (mph)


I-66 EB east of US 15 34.7 53.1

I-66 EB east of US 29 (Gainesville) 20.4 106.3



I-66 EB east of Route 234 Bypass 23.2 75.2






I-66 EB east of Rest Stop 29.2 73.4



I-66 EB east of US 29 (Centreville) 31.7 59.2

I-66 EB east of Stringfellow Rd HOV On-Ramp 34.4 55.0

I-66 EB east of Fairfax County Pkwy On-Ramp 24.7 80.9



I-66 EB west of US 50 On-Ramp 26.7 72.7

I-66 EB west of Route 243 33.5 61.1

I-66 EB west of I-495 29.7 64.3

Table 9.18: Congested Basic Freeway Segments, 2040 Preferred Alternative AM – I-66 Eastbound

Location

Preferred Alternative AM

Average Speed (mph)





I-66 EB at US 29 (Centreville) 43.4 46.3

I-66 EB west of Route 28 34.4 57.1

I-66 EB at Fairfax County Pkwy 20.3 89.9

I-66 EB east of Fairfax County Pkwy 14.3 106.4



I-66 EB at Route 123 53.3 38.5



Westbound Direction Table 9.19 provides a list of congested basic freeway segments along I-66 westbound in the 2040 No-Build AM representative hour. Only one segment in the No-Build scenario operates at a level of congestion greater than 35 vehicles per mile per lane. All other segments in the No-Build scenario, along with all basic freeway segments in the 2040 Preferred Alternative, operate at a level of congestion less than 35 vehicles per mile per lane during the AM representative hour.

Table 9.19: Congested Basic Freeway Segments, 2040 No-Build AM – I-66 Westbound

Location

No-Build AM

Average Speed (mph)


I-66 WB west of Route 123 51.9 38.3

2040 AM Weaving Segment Analysis

This section compares levels of congestion on freeway weave segments during the AM representative hour in the 2040 No-Build and 2040 Preferred Alternative scenarios.

Eastbound Direction Table 9.20 provides a list of freeway weave segments along I-66 eastbound in the 2040 No-Build AM representative hour that are congested (orange) or severely congested (red). Table 9.21 provides a list of similarly congested freeway weave segments along I-66 eastbound (general purpose lanes) in the 2040 Preferred Alternative AM representative hour. There is only one weave segment within the I-66 eastbound Express Lanes in the 2040 Preferred Alternative, located between the Route 28 Express Lanes on-ramp and the Stringfellow Road Express Lanes off-ramp. This weave segment is not congested during the AM representative hour. Note that in the design of the Preferred Alternative general purpose lanes, new freeway weaving sections are present due to the auxiliary lane provided between interchanges east of US 29 (Centreville). The weaving sections that are congested during the AM representative hour in the Preferred Alternative can be attributed to a downstream bottleneck, not the introduction of these auxiliary lanes.

Table 9.20: Congested Weave Freeway Segments, 2040 No-Build AM – I-66 Eastbound

Location

No-Build AM

Average Speed (mph)


I-66 EB west of Route 234 Bypass 17.5 101.9


I-66 EB east of Monument Dr On-Ramp 19.9 74.8



Table 9.21: Congested Weave Freeway Segments, 2040 Preferred Alternative AM – I-66 Eastbound

Location


Average Speed (mph)

Average Density

(veh/mi/ln)

I-66 EB between US 29 (Centreville) and Route 28 38.5 49.9

I-66 EB east of Route 28 14.9 95.5

I-66 EB between Route 28 and Fairfax County Pkwy 21.2 83.2



Westbound Direction In the westbound direction, all weave segments operate in an uncongested environment under the No-Build and Preferred Alternative scenarios within the general purpose lanes during the AM representative hour. In addition, within the Express Lanes, the only weave segment that exists between the Route 234 Bypass Express Lanes on-ramp and University Boulevard Express Lanes off-ramp operates in an uncongested condition. Note that in the design of the Preferred Alternative general purpose lanes, new freeway weaving sections are present due to the auxiliary lane provided between interchanges east of US 29 (Centreville).

2040 AM Ramp Junction Segment Analysis

This section compares levels of congestion on freeway ramp junction (merge or diverge) segments during the AM representative hour in the 2040 No-Build and 2040 Preferred Alternative scenarios.

Eastbound Direction Table 9.22 provides a list of freeway ramp junction segments along I-66 eastbound in the 2040 No-Build AM representative hour that are congested (orange) or severely congested (red). Table 9.23 provides a list of freeway ramp junction segments along I-66 eastbound (general purpose lanes) with similar levels of congestion in the 2040 Preferred Alternative AM representative hour. All ramp junction segments in the 2040 Preferred Alternative along the I-66 eastbound Express Lanes operate at a level of congestion below 35 vehicles per mile per lane.



Table 9.22: Congested Ramp Junction Freeway Segments, 2040 No-Build AM – I-66 Eastbound

Location Link Type

No-Build AM

Average Speed (mph)


I-66 EB west of US 29 (Gainesville) Diverge 23.7 89.1

I-66 EB east of Route 234 Bypass Merge 26.7 73.5

I-66 EB west of Route 234 Business Diverge 22.0 82.4

I-66 EB east of Route 234 Business Merge 23.4 77.2

I-66 EB west of Rest Stop Diverge 32.6 59.3

I-66 EB east of Rest Stop Merge 29.6 65.6



I-66 EB east of US 29 (Centreville) Merge 31.7 59.2



I-66 EB west of US 50 On-Ramp Merge 21.7 71.6



I-66 EB east of Route 243 Merge 33.9 51.1

I-66 EB west of I-495 Diverge 45.1 35.7

Table 9.23: Congested Ramp Junction Freeway Segments, 2040 Preferred Alternative AM – I-66 Eastbound

Location Link Type


Average Speed (mph)



I-66 EB west of ramp to I-66 Express Lanes Diverge 39.8 41.4

I-66 EB at Route 28 Merge 28.5 62.5


I-66 EB west of US 50 Diverge 18.6 87.4


Westbound Direction Table 9.24 provides a list of freeway ramp junction segments along I-66 westbound in the 2040 No-Build AM peak hour that are congested (orange) or severely congested (red). There are no congested freeway ramp junction segments along the I-66 westbound general purpose or Express Lanes in the 2040 Preferred Alternative AM representative hour.



Table 9.24: Congested Ramp Junction Freeway Segments, 2040 No-Build AM – I-66 Westbound

Location Link Type

No-Build AM

Average Speed (mph)


I-66 WB west of Fairfax County Pkwy On-Ramp Diverge 41.5 39.3

2040 AM Overall Freeway Density Results

Compared to the 2040 No-Build scenario, the Preferred Alternative is expected to operate with fewer areas of congestion in the eastbound direction along the I-66 corridor during the AM representative hour. Figure 9.27 provides a graphical comparison of the No-Build and Preferred Alternative basic freeway, weave, and ramp junction segment densities during the AM representative hour. In the No-Build scenario, a total 38 segments are expected to operate in congested or severely congested conditions. In the Preferred Alternative, only 20 segments are expected to operate under similar conditions. Although there are 9 fewer segments considered in the Preferred Alternative due to geometric enhancements, the percentage of congested segments drops from 53 percent in the No-Build scenario to just over 30 percent in the Preferred Alternative.

Figure 9.28 (a, b, c, and d) provide a geographic summary of vehicle densities along the I-66 corridor in the AM representative hour for the general purpose lanes in the No-Build and Preferred Alternative scenarios as well as the Express Lanes in the Preferred Alternative. The summary is presented for both the eastbound and westbound directions.



Figure 9.27: Summary of 2040 AM Representative Hour Segment Densities

No-Build (left) and Preferred Alternative (right)



Figure 9.28: 2040 AM Representative Hour Summary of Vehicle Densities



Figure 9.28b: 2040 AM Representative Hour Summary of Vehicle Densities



Figure 9.28c: 2040 AM Representative Hour Summary of Vehicle Densities



Figure 9.28d: 2040 AM Representative Hour Summary of Vehicle Densities



2040 AM Ramp Queues

This section compares queuing on freeway ramps during the AM peak and shoulder period in the 2040 No-Build and Preferred Alternative scenarios. Several locations in which the average and 95th percentile queue lengths exceed the available storage are expected in the No-Build scenario, while the Preferred Alternative scenario queue lengths are contained within available storage for all study area ramps.

Table 9.25 contains a list of ramps where queues exceed available storage in the AM peak and shoulder period under No-Build conditions along with the corresponding queue results in the Preferred Alternative. The reported queues result in backups onto the mainline of I-66 or adjacent arterials. This includes the eastbound I-66 off-ramps to northbound Route 28 as well as on-ramps from Fairfax County Parkway. The loop ramp from I-66 eastbound to Route 28 northbound results in more than a mile of queuing along I-66 eastbound. The Fairfax County Parkway cloverleaf interchange is another location that sees significant ramp queuing. Congestion on westbound I-66 from the Route 28 interchange impacts Fairfax County Parkway towards the end of the peak period. Queues spill back onto the westbound C-D road and on-ramps from the northbound and southbound directions. Queues on the on-ramp from northbound Fairfax County Parkway eventually congest the weave area and spill back onto the eastbound C-D road and mainline of I-66 in the shoulder period. The spillback on US 29 (Gainesville) northbound results from the on-ramp to I-66 eastbound. Since there are not any instances of a 95th percentile queue length exceeding the available storage in the Preferred Alternative, no mitigation measures are recommended. A complete table of queues on all ramps in the study area in the 2040 No-Build scenario can be found in Appendix J of the Transportation Technical Report.

Table 9.25: 2040 AM Ramps Where Average Queues Exceed Available Storage Comparison of No-Build and Preferred Alternative

Ramp Location

2040 No-Build 2040 Preferred Alternative


95th Percentile

Queue (feet)

Available Storage

(feet)


95th Percentile

Queue (feet)

Available Storage

(feet)

I-66 EB On-Ramp from US 29 (Gainesville) NB

4,129 5,335 2,348 0 0 2,348

Linton Hall Road WB to US 29 (Gainesville) NB On-Ramp

1,006 1,428 975 0 0 975

I-66 EB Off-Ramp to Route 28 NB

2,484 5,319 1,208 0 0 1,951

I-66 WB On-Ramp from Fairfax County Parkway NB

2,272 5,326 1,310 0 0 1,310

During the 2040 AM peak and shoulder period, average and 95th percentile queue lengths do not exceed the available storage in the Preferred Alternative. A complete table of queues on all ramps in the study area can be found in Appendix J of the Transportation Technical Report.

2040 AM Peak Intersection Operations

2040 AM Intersection Delay and Level of Service

This section describes the intersection and arterial performances in the study area and provides a comparison of performances during the AM representative hour between the 2040 No-Build and 2040 Preferred Alternative scenarios.



Table 9.26 provides a list of intersections with level of service E or worse during the AM representative hour for the 2040 No-Build and Preferred Alternative scenarios. A complete list of intersections in the study area along with LOS for the AM representative hour, as well as LOS for the worst hour of delay for each intersection during the AM peak and shoulder period, can be found in Appendix I of the Transportation Technical Report. Unless otherwise noted, the locations listed in Table 9.26 are signalized intersections.

Table 9.26: 2040 AM Intersections with LOS E or LOS F (7:00 – 8:00 a.m.)

Comparison of No-Build and Preferred Alternative

Figure Intersection


No-Build Preferred

Alternative

Intersection Delay

(Sec/veh) LOS

Intersection Delay

(Sec/veh) LOS

11 US 29 (Gainesville)/I-66 WB Ramps/Heathcote Blvd 137.5 F 29.6 C

9 US 29 (Gainesville) Ramps/Linton Hall Rd 387.7 F 18.6 B

14 University Blvd/Wellington Rd 34.9 C 86.2 F

87 Route 234 Bypass SB Ramps/Balls Ford Rd 15.8 B 59.6 E

20 Route 234 Business/Balls Ford Rd 164.8 F 64.8 E

21 US 29 (Centreville)/Stone Rd 64.4 E 59.1 E

66 US 29 (Centreville)/Old Centreville Rd/Braddock Rd 31.2 C 58.3 E

84 Westfields Blvd/Stonecroft Blvd 54.3 D 99.2 F



45 Route 123/Rose Forest Dr/White Granite Rd 31.5 C 55.2 E

46 Route 123/Eaton Pl/Oak Pl 37.1 D 63.7 E

99 Route 243/I-66 EB Ramps - - 56.9 E


62 Route 7/Haycock Rd/Shreve Rd 62.9 E 67.1 E

78 Route 7/I-495 Express Lanes Ramps/I-495 NB On-Ramp 64.4 E 58.5 E

79 US 29/I-495 Express Lanes Ramps 29.2 C 56.0 E

80 Gallows Rd/I-495 SB Off-Ramp/Woodburn Rd 46.4 D 57.0 E

82 Gallows Rd/I-495 Express Lanes Ramps 79.0 E 166.1 F

* Intersection ID can be found in Appendix I of TTR

Figure 9.29 provides pie charts summarizing overall intersection LOS and individual intersection approach LOS for the AM representative hour for the 2040 No-Build scenario. Figure 9.30 provides pie charts summarizing overall intersection LOS and individual intersection approach LOS for the AM representative hour for the 2040 Preferred Alternative scenario. Overall, 17 percent of intersections during the 2040 Preferred Alternative scenario operate at LOS E or worse during the AM representative hour, compared to 12 percent under No-Build conditions. The percent of approaches that operate at LOS E or worse during the AM representative hour is 21 percent in the 2040 Preferred Alternative as compared to 20 percent under No-Build conditions.



Figure 9.29: 2040 No-Build AM Representative Hour Overall Intersection and Approach LOS Summary

Figure 9.30: 2040 Preferred Alternative AM Representative Hour Overall Intersection and Approach LOS Summary

2040 AM Intersection Queues

This section briefly describes intersection queuing in the study area and provides a comparison of intersection performance during the AM representative hour between the 2040 No-Build and 2040 Preferred Alternative scenarios. Mitigating queue spillback requires a balance between accommodating 95th percentile queue lengths within the storage lane, optimization of green time at traffic signals, and minimizing construction impacts to adjacent properties to accommodate the projected vehicle queues.



Queue spillback of 10 vehicles (or 250 feet) beyond the available storage capacity of a particular movement based upon the average queue length was identified as the threshold for which consideration of geometric modifications might be warranted. This indicates a significant recurring pattern of queue spillback that could impact the safety and operations of adjacent movements.

In the No-Build scenario, a total of 26 movements exceed the available storage provided. Of these movements, eight are expected to have an average queue length that extends 250 feet or more beyond the available storage capacity. In the Preferred Alternative, a total of 43 movements exceed the available storage, of which a total of 13 movements are expected to have an average queue length that extends 250 feet or more beyond the available storage capacity. In both scenarios, the number of instances of queue spillback beyond the 10-vehicle threshold represents approximately 30 percent of all instances of queue spillback beyond the available storage. A complete list of queuing at all intersection approaches in the study area can be found Appendix I of the Transportation Technical Report.

2040 AM Intersection Considerations

A detailed description of arterial intersection minor improvements and other potential mitigation measures can be found in Sections 9.2.4 and 9.2.5 of this report. The mitigation measures provided encompass the intersection locations where LOS F is expected and queuing degradation occurs in the Build alternative but not in the No-Build scenario. If excessive delay (LOS E or worse) and queuing is expected in both scenarios beyond the 250-foot threshold, specific mitigation is not recommended. The following summarize the potential mitigation measures outlined in Sections 9.2.4 and 9.2.5 that were identified based upon the findings of the 2040 AM Preferred Alternative analyses:

University Boulevard/Wellington Road – monitor operations and consider future detailed analyses. Consider adding a westbound right-turn overlap.

Westfields Boulevard/Stonecroft Boulevard – construct an acceleration lane along Stonecroft Boulevard for the southbound right-turn lane and construct a second northbound left-turn lane.


It is worth noting that given the horizon year of the Preferred Alternative Build condition, it is plausible that traffic volumes and patterns could change from the forecast volumes for 2040. It is recommended that these locations be monitored in the future, at which point more targeted analyses and identification of mitigation measures would be more prudent.

2040 PM Peak Freeway Operations

2040 PM Travel Time Analysis

This section provides a brief overview of travel times in the 2040 No-Build and Preferred Alternative scenarios. Information is summarized for I-66 and Route 28 in both directions of travel.

Westbound Direction Travel times in the westbound direction improve for general purpose traffic and Express Lanes/HOV traffic as compared to No-Build conditions. Cumulative travel time in the general purpose lanes is reduced from 58.8 minutes to 36.4 minutes between I-495 and US 15. For general purpose traffic, average travel times in the westbound direction are shorter in the Preferred Alternative than the 2040 No-Build scenario for all segments between I-495 and US 29 (Centreville). Between US 29 (Centreville) and US 15, only a modest improvement in travel times within the general purpose travel lanes is expected in the Preferred



Alternative compared to the No-Build scenario. This is likely due to a constant metering of westbound traffic in all scenarios just west of the I-66/US 29 (Centreville) interchange.

General purpose lane travel time reductions, especially between I-495 and US 29 (Centreville), can be attributed to several factors:

The additional general purpose auxiliary lane between interchanges east of US 29 (Centreville) in the Preferred Alternative, which increases the capacity of the general purpose lanes in comparison to the No-Build configuration.

The separation of HOV traffic from general purpose traffic with flexible-post bollards in the Preferred Alternative, which eliminates the weave between general purpose and concurrent HOV lanes (this weave is possible under No-Build conditions).

The removal of traffic signals on Route 28 north of I-66, which cause queue spillback onto I-66 in both directions under No-Build conditions.


The attraction of demand to use the tolled Express Lanes facility, which has a much higher capacity than the HOV lane under No-Build conditions.

For Express Lane traffic, average travel times in the westbound direction are shorter than the 2040 No-Build scenario and the existing conditions for all segments between I-495 and US 15.

Express Lanes travel time reductions along the length of the corridor in the westbound direction can be attributed to several factors:

The separation of HOV traffic from general purpose traffic with flexible-post bollards in the Preferred Alternative, which removes the ability to weave between general purpose lanes and HOV lanes.

The increased capacity of the Express Lanes facility due to the bollard separation, second travel lane, and posted speed limit of 65 mph along the entire 25-mile corridor.

Figure 9.31 shows a comparison of cumulative and incremental travel times along I-66 westbound through the study area during the PM peak period. This figure provides a comparison between the 2040 Preferred Alternative, 2040 No-Build, and existing conditions. The figure differentiates between Express Lanes/HOV and general purpose traffic in each scenario.



Figure 9.31: 2040 Preferred Alternative, 2040 No-Build, and Existing PM Travel Time Comparison – I-66 Westbound



Eastbound Direction In the eastbound direction, travel times between US 15 and US 50 remain relatively unchanged between the 2040 Preferred Alternative and 2040 No-Build scenarios. East of US 50, the Preferred Alternative sees slightly higher travel times due to occasional queue spillback from the ramp to I-495 southbound. In 2040, capacity improvements on I-495 southbound north of I-66 allow more volume to travel south toward its interchange with US 50. In the Preferred Alternative simulations, the weave area on I-495 southbound between I-66 and US 50 would occasionally cause queues to spill back onto I-66 eastbound, resulting in slower speeds. While this congestion is not observed in the No-Build scenario, it should be noted that some traffic along I-66 eastbound in the No-Build scenario may be constrained upstream due to a bottleneck at Route 28. Should these queues occur, drivers heading eastbound on I-66 under the Preferred Alternative will have the option to use the I-66 Express Lanes to access the I-495 southbound Express Lanes and avoid backups on I-66 eastbound and I-495 southbound. Motorists will have the opportunity to access the I-66 eastbound Express Lanes from the eastbound general purpose lanes by way of a flyover ramp just west of I-495 if not already traveling within the Express Lanes. Travel times on I-66 eastbound Express Lanes/HOV are lower than travel times in the general purpose lanes in the Preferred Alternative and No-Build conditions due to the posted 65 mph speed limit.

Figure 9.32 shows a comparison of cumulative and incremental travel times along I-66 eastbound through the study area during the PM peak period.



Figure 9.32: 2040 Preferred Alternative, 2040 No-Build, and Existing PM Travel Time Comparison – I-66 Eastbound



Route 28 Travel times along Route 28 improve in both the northbound and southbound directions in the Preferred Alternative as compared to No-Build conditions. In the northbound direction, average travel times from US 29 (Centreville) to Westfields Boulevard are approximately 3 minutes, which represents a travel time reduction of 1 minute when compared to No-Build conditions. In the southbound direction along the same section of Route 28, average travel times drop by 400 percent from 12 minutes in the No-Build condition to approximately 3 minutes in the Preferred Alternative. This reduction can be attributed to the removal of existing traffic signals and improved ramp access to and from I-66.

2040 PM Speed Analysis

Figure 9.33 illustrates the PM peak period 15-minute average speeds along I-66 westbound in 15-minute increments for existing, 2040 No-Build, and 2040 Preferred Alternative conditions. Traffic speeds improve under the Preferred Alternative condition in comparison to the existing and No-Build conditions along both the eastbound and westbound I-66 corridor. Figure 9.34 depicts a similar speed contour graphic for the eastbound direction.

In the PM peak period, the figures demonstrate that speeds along I-66 westbound slow to less than 20 mph approaching the bottleneck just west of the interchange with US 29 (Centreville) during the representative hour. Over the course of the next few hours in the peak period, this bottleneck extends backwards, reaching nearly to Route 243 (Nutley Street) by the end of the peak period. Downstream of US 29 (Centreville), speeds are between 35 and 50 mph before slowing to less than 35 mph between the Rest Area and Route 234 Business. West of Route 234 Business, speeds increase and are consistently above 60 mph west of Route 234 Bypass.

Unlike the AM peak period, the eastbound direction of travel in the PM peak period is expected to operate with periods and segments of reduced travel speeds. As shown in Figure 9.34, speeds are greater than 50 mph until reaching US 50 during the representative hour. Between US 50 and I-495, speeds range between 35 and 50 mph. As the peak period progresses, speeds between Stringfellow Road and US 50 also slow to between 35 and 50 mph. These slowdowns can be attributed to queue spillback stemming from the ramp from I-66 eastbound to I-495 southbound. Although densities are high through this stretch of the eastbound lanes of I-66, speeds have not slowed to a standstill. This suggests that there is some variability in the formation of queues from the ramp to I-495 southbound, and in some situations, these queues may not be present.


Along Route 28, average speeds are at or near the posted speed limit in both directions. Between Braddock Road and US 29, the Route 28 mainline was modeled at a 45 mph speed limit, while north of this location, the speed limit was posted as 55 mph. Improvements in average speeds in the Preferred Alternative scenario can be attributed to the removal of traffic signals and enhancements to interchange access to and from I-66 that are otherwise not present in the No-Build scenario.



Figure 9.33: 2040 Preferred Alternative PM Peak Period Speed Comparison – I-66 Westbound General Purpose Lanes



Figure 9.34: 2040 Preferred Alternative PM Peak Period Speed Comparison – I-66 Eastbound General Purpose Lanes

2040 PM Basic Freeway Segment Analysis

This section compares levels of congestion on basic freeway segments during the PM representative hour between the 2040 No-Build and 2040 Preferred Alternative scenarios.

Westbound Direction Table 9.27 provides a list of basic freeway segments along I-66 westbound in the 2040 No-Build PM representative hour that are congested (orange) or severely congested (red). Table 9.28 provides a list of basic freeway segments along I-66 westbound (general purpose lanes) in the 2040 Preferred Alternative PM representative hour with similar levels of congestion.



Table 9.27: Congested Basic Freeway Segments, 2040 No-Build PM – I-66 Westbound

Location

No-Build PM

Average Speed (mph)

Average Density

(veh/mi/ln)

I-66 WB west of I-495 46.6 40.3

I-66 WB west of I-495 39.6 47.8


I-66 WB west of Route 243 16.3 102.7

I-66 WB west of Route 243 15.8 102.6

I-66 WB east of Route 123 15.6 106.0



I-66 WB west of Fairfax County Pkwy On-Ramp 29.1 60.6



I-66 WB east of Route 234 Business 43.5 44.8

Table 9.28: Congested Basic Freeway Segments, 2040 Preferred Alternative PM – I-66 Westbound

Location

Preferred Alternative PM

Average Speed (mph)

Average Density

(veh/mi/ln)

I-66 WB at Fairfax County Pkwy 47.6 42.1


I-66 WB at Route 28 18.9 84.5


I-66 WB west of US 29 (Centreville) 46.2 47.9


Eastbound Direction Table 9.29 provides a list of congested basic freeway segments along I-66 eastbound in the 2040 No-Build PM representative hour. Only one freeway segment in the eastbound direction operates at a level of severe congestion (red) during the PM representative hour in the No-Build condition. Table 9.30 provides a list of basic freeway segments along I-66 eastbound (general purpose lanes) in the 2040 Preferred Alternative PM representative hour that are congested (orange) or severely congested (red). There are no congested basic freeway segments along the I-66 eastbound Express/HOV lanes in the 2040 Preferred Alternative PM representative hour.



Table 9.29: Congested Basic Freeway Segments, 2040 No-Build PM – I-66 Eastbound

Location

No-Build PM

Average Speed (mph)


I-66 EB east of Dulles Toll Rd 9.4 71.0

Table 9.30: Congested Basic Freeway Segments, 2040 Preferred Alternative PM – I-66 Eastbound

Location


Average Speed (mph)




I-66 EB at Route 123 43.6 50.2

I-66 EB at Route 243 41.5 54.7

I-66 EB east of Route 243 40.4 56.0

I-66 EB east of Ramp to I-66 Express Lanes 37.6 61.4

2040 PM Weaving Segment Analysis

This section compares levels of congestion on freeway weave segments during the PM representative hour in the 2040 No-Build and 2040 Preferred Alternative scenarios.

Westbound Direction In the 2040 No-Build PM representative hour, all weave segments operate at a level of congestion below 35 vehicles per mile per lane. Similar levels of congestion are not expected in the Preferred Alternative. Table 9.31 provides a list of congested freeway weave segments along I-66 westbound (general purpose lanes) in the 2040 Preferred Alternative PM representative hour that are congested (orange) or severely congested (red). There is only one weave segment within the I-66 westbound Express Lanes in the 2040 Preferred Alternative, located between the Route 234 Bypass Express Lanes on-ramp and the University Boulevard Express Lanes off-ramp. This weave segment is not congested during the PM representative hour. Note that in the design of the Preferred Alternative general purpose lanes, new freeway weaving sections are present due to the auxiliary lane provided between interchanges east of US 29 (Centreville). The weaving sections that are congested during the PM representative hour in the Preferred Alternative can be attributed to a downstream bottleneck, not the introduction of these auxiliary lanes.



Table 9.31: Congested Weave Freeway Segments, 2040 Preferred Alternative PM – I-66 Westbound

Location


Average Speed (mph)

Average Density

(veh/mi/ln)

I-66 WB between Route 123 and US 50 53.7 35.3

I-66 WB between Fairfax County Pkwy and Route 28 40.1 42.3

I-66 WB between I-66 WB Express Lane Ramps near Route 28 28.9 57.7

I-66 WB between Route 28 and US 29 (Centreville) 15.3 92.8

Eastbound Direction In the eastbound direction, all weave segments operate in an uncongested environment under the No-Build and Preferred Alternative scenarios within the general purpose lanes during the PM representative hour. In addition, within the Express Lanes, the only weave segment that exists between the Route 28 Express Lanes on-ramp and the Stringfellow Road Express Lanes off-ramp operates in an uncongested condition. Note that in the design of the Preferred Alternative general purpose lanes, new freeway weaving sections are present due to the auxiliary lane provided between interchanges east of US 29 (Centreville).

Table 9.32: Congested Weave Freeway Segments, 2040 Preferred Alternative PM – I-66 Eastbound

Location


Average Speed (mph)

Average Density

(veh/mi/ln)



2040 PM Ramp Junction Segment Analysis

This section compares levels of congestion on freeway ramp junction (merge or diverge) segments during the PM representative hour in the 2040 No-Build and 2040 Preferred Alternative scenarios.

Westbound Direction Table 9.33 provides a list of freeway ramp junction segments along I-66 westbound in the 2040 No-Build PM representative hour that are congested (orange) or severely congested (red). Table 9.34 provides a list of freeway ramp junction segments along I-66 westbound (general purpose lanes) in the 2040 Preferred Alternative PM representative hour that operate at similar levels of congestion. There are no congested freeway ramp junction segments along the I-66 westbound Express Lanes in the 2040 Preferred Alternative PM representative hour.



Table 9.33: Congested Ramp Junction Freeway Segments, 2040 No-Build PM – I-66 Westbound

Location Link Type

No-Build PM

Average Speed (mph)




I-66 WB west of Vaden Dr On-Ramp Merge 11.1 117.3




I-66 WB between Fairfax County Pkwy Off-Ramp and On-Ramp Diverge 21.3 76.4

I-66 WB west of Fairfax County Pkwy On-Ramp Merge 27.9 62.2

I-66 WB west of Fairfax County Pkwy On-Ramp Diverge 28.0 62.2

I-66 WB west of Route 28 Off-Ramp Diverge 26.4 64.0




I-66 WB west of Rest Stop Merge 41.2 40.9

I-66 WB east of Route 234 Business Diverge 42.0 42.5

I-66 WB east of Route 234 Business Diverge 39.6 48.9

Table 9.34: Congested Ramp Junction Freeway Segments, 2040 Preferred Alternative PM – I-66 Westbound

Location Link Type


Average Speed (mph)

Average Density

(veh/mi/ln)

I-66 WB east of Fairfax County Pkwy Diverge 43.0 38.5

I-66 WB at Route 28 Diverge 22.0 71.1




I-66 WB west of Rest Stop Merge 46.7 37.2

Eastbound Direction Table 9.35 provides a list of freeway ramp junction segments along I-66 eastbound in the 2040 No-Build PM representative hour that are congested (orange) or severely congested (red). Table 9.36 provides a list of congested freeway ramp junction segments along I-66 eastbound (general purpose lanes) in the 2040 Preferred Alternative PM representative hour that operate under similar levels of congestion. There



are no congested freeway ramp junction segments along the I-66 eastbound Express Lanes in the 2040 Preferred Alternative PM representative hour.

Table 9.35: Congested Ramp Junction Freeway Segments, 2040 No-Build PM – I-66 Eastbound

Location Link Type

No-Build PM

Average Speed (mph)

Average Density

(veh/mi/ln)



Table 9.36: Congested Ramp Junction Freeway Segments, 2040 Preferred Alternative PM – I-66 Eastbound

Location Link Type


Average Speed (mph)

Average Density

(veh/mi/ln)

I-66 EB east of Route 243 On-Ramp Merge 40.9 42.7

I-66 EB west of Ramp to I-66 Express Lanes Diverge 39.2 54.4

I-66 EB west of I-495 Diverge 36.9 57.7

2040 PM Overall Freeway Density Results

Compared to the 2040 No-Build scenario, the Preferred Alternative is expected to operate with fewer areas of congestion in the westbound direction along the I-66 corridor during the PM representative hour. Figure 9.35 provides a graphical comparison of the No-Build and Preferred Alternative basic freeway, weave, and ramp junction segment densities during the PM representative hour. In the No-Build scenario, a total of 28 segments are expected to operate in congested or severely congested conditions. In the Preferred Alternative, only 16 segments are expected to operate under similar conditions. Although there are six fewer segments considered in the Preferred Alternative due to geometric enhancements, the percentage of congested segments drops from 36 percent in the No-Build scenario to just over 22 percent in the Preferred Alternative.

Figure 9.36 (a, b, c, and d) provides a geographic summary of vehicle densities along the I-66 corridor in the PM representative hour for the general purpose lanes in the No-Build and Preferred Alternative scenarios as well as the Express Lanes in the Preferred Alternative. The summary is presented for both eastbound and westbound directions.



Figure 9.35: Summary of 2040 PM Representative Hour Segment Densities

No-Build (left) and Preferred Alternative (right)



Figure 9.36: 2040 PM Representative Hour Summary of Vehicle Densities



Figure 9.36b: 2040 PM Representative Hour Summary of Vehicle Densities



Figure 9.36c: 2040 PM Representative Hour Summary of Vehicle Densities



Figure 9.36d: 2040 PM Representative Hour Summary of Vehicle Densities



2040 PM Ramp Queues

This section compares queuing on freeway ramps during the PM peak and shoulder period in the 2040 No-Build and Preferred Alternative scenarios. Several locations in which the average and 95th percentile queue lengths exceed the available storage are expected in the No-Build scenario. In the Preferred Alternative, only one location is expected to operate with average and 95th percentile queue lengths that exceed the available storage, and it is not a ramp location to or from I-66. Another ramp junction not tied to I-66 is expected to have a 95th percentile queue length greater than the available storage in the Preferred Alternative. The southbound West Ox Road on-ramp to US 50 eastbound queue exceeds the available storage by 450 feet, but the average queue is nearly 10 percent of the 95th percentile queue and is more than accommodated by the available storage.

Table 9.37 contains a list of ramps where queues exceed available storage in the PM peak and shoulder period under No-Build conditions along with the corresponding queue results in the Preferred Alternative. The reported queues result in backups onto the mainline of I-66 or adjacent arterials. This includes the eastbound I-66 off-ramps to southbound Route 234 Business and southbound Route 28 as well as on-ramps from Fairfax County Parkway. The spillback at Route 234 Business is caused by the signal operations at the Balls Ford Road and I-66 eastbound ramp intersection. Congestion on southbound US 29 (Centreville) causes spillback onto southbound Route 28, with subsequent queue spillback onto I-66 westbound. The signalized intersections along Route 28 north of I-66 cause southbound queue spillback onto Westfields Boulevard. The Fairfax County Parkway cloverleaf interchange is another location that experiences significant ramp queuing. Congestion on westbound I-66 from the Route 28 interchange impacts Fairfax County Parkway towards the end of the peak period. Queues spill back onto the westbound C-D road and on-ramps from the northbound and southbound directions. Queues along the on-ramp from northbound Fairfax County Parkway affect the weave area and spill back onto the eastbound C-D road and mainline of I-66 in the shoulder period. Since these locations in the Preferred Alternative are outside of the IJR study area, no mitigation measures are recommended at these locations. A complete table of queues on all ramps in the study area in the 2040 No-Build scenario can be found in Appendix J of the Transportation Technical Report.



Table 9.37: 2040 PM Ramps Where Average Queues Exceed Available Storage

Comparison of No-Build and Preferred Alternative

Ramp Location

2040 No-Build 2040 Preferred Alternative


95th Percentile

Queue (feet)

Available Storage

(feet)


95th Percentile

Queue (feet)

Available Storage

(feet)

I-495 NB On-Ramp from US 50 WB

376 3,281 725 1,004 5,269 725

I-66 WB Off-Ramp to Route 234 Business SB

2,146 5,313 1,223 0 0 3,900

I-66 WB Off-Ramp to Route 28 SB

3,465 5,334 1,573 134 49 1,124

Route 28 SB Off-Ramp to US 29 (Centreville) SB

1,796 2,418 1,188 104 537 1,188

Route 28 C-D south of Westfields Boulevard

1,532 2,329 1,285 6 0 1,285

I-66 EB Off-Ramp to Fairfax County Parkway NB

1,820 5,325 1,512 4 0 1,512

I-66 WB On-Ramp from Fairfax County Parkway

1,741 3,268 1,335 39 69 2,421

I-66 WB On-Ramp from Fairfax County Parkway NB

2,056 5,334 1,310 13 0 1,310

I-66 WB On-Ramp from Fairfax County Parkway SB

2,460 5,330 2,134 15 0 2,134

West Ox Road SB to US 50 EB Ramp

1,459 2,725 939 168 1,396 939

2040 PM Peak Intersection Operations

2040 PM Intersection Delay and Level of Service

This section describes the intersection and arterial performances in the study area and provides a comparison of performances during the PM representative hour between the 2040 No-Build and 2040 Preferred Alternative scenarios.

Table 9.38 provides a list of intersections with level of service E or worse during the PM representative hour for the 2040 No-Build and Preferred Alternative scenarios. A complete list of intersections in the study area along with LOS for the PM representative hour, as well as LOS for the worst hour of delay for each intersection during the PM peak period, can be found in Appendix I of the Transportation Technical Report. Unless otherwise noted, the locations listed in Table 9.38 are signalized intersections.



Table 9.38: 2040 PM Intersections with LOS E or LOS F (4:30 – 5:30 p.m.)

No-Build and Preferred Alternative

Figure Intersection


No-Build Preferred

Alternative Intersection

Delay (Sec/veh)

LOS Intersection

Delay (Sec/veh)

LOS

12 US 29 (Gainesville)/University Blvd 57.6 E 83.2 F

9 US 29 (Gainesville) Ramps/Linton Hall Rd 50.8 D 55.2 E

14 University Blvd/Wellington Rd 78.2 E 68.9 E

86 Route 234 Bypass NB Ramps/Balls Ford Rd 55.6 E 66.2 E

16 Route 234 Business/Bullock Dr/Battleview Pkwy 138.6 F 50.7 D

17 Route 234 Business/I-66 WB On-Ramp/Vandor Lane 58.7 E 27.8 C

18 Route 234 Business/I-66 EB Ramps 69.5 E 14.4 B

20 Route 234 Business/Balls Ford Rd 91.1 F 54.7 D

21 US 29 (Centreville)/Stone Rd 121.2 F 114.5 F

23 US 29 (Centreville)/I-66 WB Ramps 61.2 E 33.8 C

24 US 29 (Centreville)/I-66 EB Ramps 131.9 F 31.0 C

25 US 29 (Centreville)/Trinity Pkwy/Machen Rd 103.8 F 43.0 D

64 US 29 (Centreville)/Route 28 SB On-Ramp/Newgate Shopping Center Entrance

94.1 F 31.9 C

66 US 29 (Centreville)/Old Centreville Rd/Braddock Rd 143.6 F 64.2 E

83 Westfields Blvd/Park Meadow Dr/Newbrook Dr 85.0 F 176.8 F

84 Westfields Blvd/Stonecroft Blvd 118.9 F 77.3 E

26 Route 28/Ellanor C. Lawrence Park 184.2 F - -

27 Route 28/Braddock Rd/Walney Rd 94.3 F 43.0 D

29 Route 28/I-66 EB On-Ramp/Sully Senior Center 107.7 F - -

30 Stringfellow Rd/Fair Lakes Blvd 48.6 D 57.9 E

77 West Ox Rd/US 50 EB Off-Ramp 74.0 E 14.9 B

40 US 50/Fair Lakes Mall Entrance (West)** 250.6 F 22.3 C

41 US 50/Fair Lakes Mall Entrance (East)** 97.7 F 10.4 B


43 US 50/Jermantown Rd 112.8 F 100.8 F


46 Route 123/Eaton Pl/Oak Pl 33.7 C 153.0 F

47 Route 123/US 50/US 29 87.1 F 92.1 F

56 Route 243/US 29 97.7 F 102.4 F


58 Route 7/I-66 EB Ramps 161.4 F 57.8 E

59 Route 7/Metrorail Lot/Dale Dr** 44.6 E 5.9 A



Figure Intersection


No-Build Preferred

Alternative Intersection

Delay (Sec/veh)

LOS Intersection

Delay (Sec/veh)

LOS

60 Route 7/Mary Ellen Henderson MS Entrance/Chestnut St**

46.1 E 9.9 A

61 Route 7/ George Mason HS Entrance/Chestnut St** 66.4 F 13.4 B

62 Route 7/Haycock Rd/Shreve Rd 121.0 F 75.4 E

80 Gallows Rd/I-495 SB Off-Ramp/Woodburn Rd 187.1 F 201.2 F * Intersection ID can be found in Appendix I of the TTR ** Unsignalized intersection

Figure 9.37 provides pie charts summarizing overall intersection LOS and individual intersection approach LOS for the PM representative hour for the 2040 No-Build scenario. Figure 9.38 provides pie charts summarizing overall intersection LOS and individual intersection approach LOS for the PM representative hour for the 2040 Preferred Alternative scenario. Overall, 19 percent of intersections during the 2040 Preferred Alternative scenario operate at LOS E or worse during the PM representative hour, compared to 36 percent under No-Build conditions. The percent of approaches that operate at LOS E or worse during the PM representative hour is 27 percent in the 2040 Preferred Alternative in comparison to 35 percent under No-Build conditions.

Figure 9.37: 2040 No-Build PM Representative Hour Intersection LOS Summary



Figure 9.38: 2040 Preferred Alternative PM Representative Hour Intersection LOS Summary

2040 PM Intersection Queues

This section briefly describes intersection queuing in the study area and provides a comparison of intersection performance during the PM representative hour between the 2040 No-Build and 2040 Preferred Alternative scenarios. Queue spillback of 10 vehicles (or 250 feet) beyond the available storage capacity of a particular movement based upon the average queue length was identified as the threshold for which consideration of geometric modifications might be warranted. This indicates a significant recurring pattern of queue spillback that could impact the safety and operations of adjacent movements.

In the No-Build scenario, a total of 72 movements exceed the available storage provided. Of these movements, 34 are expected to have an average queue length that extends 250 feet or more beyond the available storage capacity. In the Preferred Alternative, a total of 60 movements exceed the available storage, of which a total of 22 movements are expected to have an average queue length that extends 250 feet or more beyond the available storage capacity. The number of instances of queue spillback beyond the 10-vehicle threshold drops from 47 percent of all instances in the No-Build scenario to less than 40 percent of all instances of queue spillback beyond the available storage in the Preferred Alternative.

2040 PM Intersection Considerations

A detailed description of arterial intersection minor improvements and other potential mitigation measures can be found in Sections 9.2.4 and 9.2.5 of this report. The mitigation measures provided encompass the intersection locations where LOS F is expected and queuing degradation occurs in the Build alternative but not in the No-Build scenario. If excessive delay (LOS E or worse) and queuing is expected in both scenarios beyond the 250-foot threshold, specific mitigation is not recommended. The following summarize the potential mitigation measures outlined in Sections 9.2.4 and 9.2.5 that were identified based upon the findings of the 2040 PM Preferred Alternative analyses:



US 29 (Gainesville)/University Boulevard – monitor operations and consider future detailed analyses, especially in light of travel pattern changes that could result from the construction of the Bi-County Parkway.

University Boulevard/I-66 Express Lanes – provide exclusive westbound left- and right-turn lanes from the off-ramp.

Westfields Boulevard/Park Meadow Drive – monitor operations and consider future detailed analyses, including the downstream interchange with Route 28.


It is worth noting that given the horizon year of the Preferred Alternative Build condition, it is plausible that traffic volumes and patterns could change from the forecast volumes for 2040. It is recommended that these locations be monitored in the future, at which point more targeted analyses and identification of mitigation measures would be more prudent.

9.2.4 Intersection Traffic Signal Operations Mitigation Considerations The I-66 Corridor Improvements Project will bring corridor-wide changes to the transportation network. The freeway will largely be repurposed to consistently provide two Express Lanes and a minimum of three general purpose lanes in each direction, maintaining similar access to and from the general purpose lanes at existing interchanges. The impact to arterial operations under Build conditions will be in the form of changes in travel patterns as well as modified or new access to I-66, primarily for entry and egress from the Express Lanes. The following are brief descriptions of the arterial locations where new access is to be provided along with the associated intersection geometry and operations. The network adjustments described in this section were included in the analysis of the Build condition models, and unless otherwise stated, the proposed geometry will be implemented as part of Phase 1 of the I-66 Corridor Improvements Project.



Haymarket Park-and-Ride I-66 Express Lane Ramps

The intersection at the Express Lane access point in Haymarket under the Preferred Alternative will be configured to provide one exclusive lane for each allowable movement with the exception of the southbound right-turn movement, which will be shared with the through movement (see Figure 9.39). The Haymarket park-and-ride lot will be built by others through a separate but coordinated project. The Express Lane intersection will be located on a new roadway between Heathcote Boulevard and John Marshall Highway, passing over I-66 to the west of US 15. The final alignment will be determined after the construction of Phase 1 improvements based upon demonstrated need. The roadway is assumed to be a two-lane collector with a posted speed limit of 35 mph. The forecast peak-period volumes indicate the primary travel pattern is from northbound to eastbound in the AM peak period and westbound to southbound in the PM peak period. Given the proposed intersection geometry, which was developed based on forecast demand, a four-lane section is required south of I-66.

Figure 9.39: Haymarket Park-and-Ride I-66 Express Lane Ramps



University Boulevard at I-66 Express Lane Ramps

Access to the I-66 Express Lanes will be provided to and from the east along a bidirectional ramp that connects with University Boulevard at a signalized intersection. In Phase 1, intersection geometry will be configured to provide a single-lane approach from the off-ramp (shared left and right-turn lane) and a single lane each for the southbound left-turn and northbound right-turn, as well as two lanes in each direction along University Boulevard (see Figure 9.40a). In the Preferred Alternative, the PM peak period off-ramp volumes warrant exclusive left- and right-turn lanes to mitigate potential queuing onto the Express Lanes (see Figure 9.40b). In the Preferred Alternative, dual westbound left-turn lanes are recommended in order to mitigate queuing along the off-ramp and University Boulevard in the PM peak period. As previously mentioned, signals along University Boulevard will operate in a coordinated pattern to control platoon progression between US 29 (Gainesville) and I-66 given the close intersection spacing. Due to the controlled progression, the southbound volume destined for the Express Lanes is metered and can be processed onto the Express Lanes in a single southbound left-turn lane. The same is expected for the northbound and westbound right-turn movements.

Figure 9.40: University Boulevard at I-66 Express Lane Ramps *

a. Phase 1 b. Preferred Alternative

*The configurations shown reflect the original Phase 1 and Preferred Alternative prior to revisions for mitigation measures. See Section 9.2.5 for the latest proposed geometric mitigations.



Route 234 Bypass Park-and-Ride I-66 Express Lane Ramps

In the Preferred Alternative, direct access will be provided to and from the I-66 Express Lanes at the Route 234 Bypass park-and-ride lot at an unsignalized intersection (see Figure 9.41). Arterial access to and from the lot is provided by way of Cushing Road, a local roadway that carries low traffic volumes. Given the limited demand along this roadway, the number of conflicts per hour at the proposed access ramp are low, supporting the stop-controlled operation of the intersection. It is assumed that stop control is provided for the park-and-ride lot and Express Lane ramp terminus. This results in a ramp profile of three lanes at the intersection, with two lanes exiting the Express Lanes and one lane entering. Configuration of access to the proposed site by others will be determined at a later date based upon a final approved site plan.

Figure 9.41: Route 234 Bypass Park-and-Ride I-66 Express Lane Ramps



Balls Ford Road Park-and-Ride I-66 Express Lane Ramps

Express Lane access will be provided from Balls Ford Road with a park-and-ride facility access point along the ramp located approximately 1,500 feet from the intersection with Balls Ford Road. The location of the park-and-ride facility to the east of the Express Lane access ramp requires that the park-and-ride facility access point be signalized. This is warranted by volume of exiting traffic during the PM peak period that would be in conflict with the Express Lanes off-ramp traffic destined for Balls Ford Road. Exclusive westbound left- and right-turn lanes are provided for egress from the park-and-ride lot based on forecast demand (see Figure 9.42a).

At the intersection with Balls Ford Road, dual eastbound left-turn and southbound left-turn lanes are necessary to process the forecast volumes to and from the Express Lanes. The number of turn lanes also increases the capacity of the movement, reducing the green-time allocation and allowing the heavy westbound right-turn movement volume to operate in a single right-turn lane with an overlap phase. The intersection configurations described also assume Balls Ford Road to be a four-lane roadway in future-year conditions. The forecast volume at Notes Drive is low and does not warrant any modifications to the existing geometry. An exclusive left-turn lane is recommended given the volume of opposing traffic and limited sight distance created by the dual eastbound left-turn lanes. The ramp profile at the intersection with Balls Ford Road requires a minimum of five lanes. A four-lane section will be necessary in order to allow merging of traffic past the park-and-ride facility access point, but the geometry can taper down to a two-lane section for the portion of the ramp traveling over the I-66 travel lanes (see Figure 9.42a and Figure 9.42b).

Figure 9.42: Balls Ford Road Park-and-Ride I-66 Express Lane Ramps

a. Park-and-Ride Access b. Balls Ford Road



Braddock Road at Route 28

Route 28 is converted from a signalized arterial to a limited-access facility between US 29 (Centreville) and Westfields Boulevard. The proposed improvements grade separate the intersection with Braddock Road, and a bifurcated interchange allows for all movements to and from I-66 to be free-flow, eliminating the need for the current interchange signals. Turning volumes to and from Braddock Road and Route 28 to the south are forecast to be more than 1,000 vehicles per hour during the AM and PM peak periods, with minimal volume traveling along Braddock Road. As such, single through lanes are sufficient at this intersection, while dual eastbound right and northbound left-turn lanes are required to process the forecast demand. The configuration of the interchange is such that southbound Route 28 travel lanes separate the alignment of the off- and on-ramps to Route 28. The off-ramp terminal intersecting with Braddock Road will have a ramp profile of three lanes, while the on-ramp will have a ramp profile of two lanes (see Figure 9.43).

Figure 9.43: Braddock Road at Route 28



Stringfellow Road at I-66 Express Lane Ramps

In Phase 1, the interchange geometry at Stringfellow Road will make use of the existing directional ramp in the median of I-66 for Express Lanes on-ramp traffic, and a new directional ramp will be constructed on the north side of I-66 for Express Lanes off-ramp traffic. The two ramp terminals will operate as individual signalized intersections in a coordinated environment, with the I-66 westbound general purpose (blue) and Express Lanes (orange) passing over Stringfellow Road in between the two traffic signals (see Figure 9.44a). In the Preferred Alternative, the median ramp for on-ramp traffic will be eliminated for future transit purposes and a new on-ramp will be constructed adjacent to the Phase 1 westbound off-ramp (see Figure 9.44b). The forecast traffic volumes for access to and from the Express Lanes are relatively low and are adequately served by single-lane turning movements at the proposed traffic signals, retaining the two lanes in each direction along Stringfellow Road. This results in a ramp profile of three lanes at the intersection in the Preferred Alternative.

Figure 9.44: Stringfellow Road at I-66 Express Lane Ramps


Monument Drive at I-66 Express Lane Ramps

Full access to and from the Express Lanes will be provided at Monument Drive. In Phase 1, access will be limited to a single on- and off-ramp lane (two-lane ramp profile) in the existing median of I-66. The current east-facing ramp will be retained, and a similar west-facing ramp will be constructed to accommodate access to the west. The forecast traffic volumes at the intersection indicate a predominant morning travel pattern eastbound from the ramps to southbound Monument Drive, with a reverse commute pattern in the evening. To optimize the allocation of green time to these movements, reconfiguration of the geometry along Monument Drive is recommended. The third northbound departure lane along Monument Drive is recommended to be repurposed as a southbound left-turn onto the eastbound Express Lanes, which allows for two through lanes and one exclusive right-turn lane in the southbound direction (see Figure 9.45a). In the Preferred Alternative, access to the Express Lanes within the median of I-66 is eliminated and new ramps are proposed to tie into Monument Drive to the north of I-66. The same intersection geometry as Phase 1 is proposed with the exception of the off-ramp movements. Exclusive left- and right-turn lanes are recommended, resulting in a ramp profile of three lanes (see Figure 9.45b).



Today, the Monument Drive corridor operates in an uncoordinated pattern, with the intersections at Fair Lakes Parkway, the I-66 HOV ramp, and Government Center Parkway operating independently from each other. With the increased demand along Monument Drive, there is a need for controlled progression of vehicles as they travel to and from the Express Lane ramps. As such, the corridor was adjusted to operate coordinated patterns during the peak periods. In Phase 1, the ramps must operate independently of each other given the single-lane approach serving both turning movements and to avoid conflict among opposing left- and right-turn traffic. In the Preferred Alternative, to reduce the amount of green time allocated to the ramps, it is recommended that the off-ramp left-turn movements run concurrently and the right-turn movements operate as overlapping phases to the Monument Drive left-turn movements onto the Express Lane ramps.

Figure 9.45: Monument Drive at I-66 Express Lane Ramps




US 50 at I-66 Express Lane Ramps

Interchange geometry at the Express Lanes provides direct ramp access to and from the east. The arterial roadway network has been configured to provide exclusive deceleration and acceleration lanes to and from the Express Lanes (see Figure 9.46). Therefore, intersection control is not required at this location, and arterial operations should be impacted minimally by these access points.

Figure 9.46: US 50 at I-66 Express Lane Ramps



Route 123 at I-66 Express Lane Ramps

Direct access to the Express Lanes will be provided at Route 123 for motorists traveling to and from the east. The point of access will be located in the center median of I-66 with space reserved for future transit purposes (yellow), thereby separating the on- and off-ramps by approximately 50 feet (see Figure 9.47). Forecast traffic volumes using the Express Lanes on- and off-ramps are primarily oriented to the south, with hourly volumes of more than 300 vehicles during the AM and PM peak period traveling in the peak direction. Given the demand oriented to the south, dual westbound left-turn lanes were provided at the intersection. Due to geometric constraints, right-turn movements are shared with the adjacent movements in the northbound and westbound directions to reduce bridge footprints and widening. An exclusive southbound left-turn lane is provided to separate queued vehicles from the through travel lanes. Located less than 2,000 feet from signalized intersections to the north and south on Route 123, the signal was programmed to operate at a coordinated cycle length identical to the other signals along the corridor.

Figure 9.47: Route 123 at I-66 Express Lane Ramps



Vaden Drive at I-66 Express Lane Ramps

Express Lane access at Vaden Drive is provided in the Build condition. Express Lane off-ramp hourly volumes exceed 600 vehicles during the AM peak period, with traffic primarily oriented to the south. A similar reverse commuting pattern is evident in the PM peak period. Moderate traffic volumes along Vaden Drive and the Express Lanes ramp allow the intersection to operate well with single exclusive turn lanes for the eastbound left- and right-turn movements as well as the northbound left-turn movement. To minimize bridge width, the southbound right-turn movement is shared with the rightmost through lane. Today, the signals along Vaden Drive operate in an uncoordinated pattern. Given the close intersection spacing over a short distance in the Build condition, the traffic signals were evaluated as part of a coordinated system. The ramp profile evaluated included two approach lanes and two departure lanes from the intersection (four total - see Figure 9.48). However, given that the turning movements onto the Express Lanes are single-lane movements, the departure could be reduced to a single lane.

Figure 9.48: Vaden Drive at I-66 Express Lane Ramps

The assumptions for intersections serving the I-66 Express Lanes were made using the forecast traffic volumes to optimize signal operations and minimize queuing along the ramps. The total number of travel lanes along the ramp at its intersection with the arterial are provided above as an approximate indication of the ramp footprint. As part of the Preferred Alternative analysis, it was determined that the preliminary design concepts provide sufficient capacity for all Express Lanes access to mitigate queuing impacts with the exception of two locations. At Monument Drive, the Phase 1 design will result in peak period ramp queuing that could approach the mainline Express Lanes at the height of congestion. The Preferred Alternative design at this location should not result in queuing onto the mainline, but strategic signal



operations may be required to mitigate potential queuing. At University Boulevard, the Phase 1 design will result in peak period ramp queuing that could approach the mainline Express Lanes at the height of congestion. If the intersection footprint identified above is not implemented as part of the Preferred Alternative, substantial queuing onto the mainline and heavy congestion along University Boulevard can be expected based upon forecast traffic volumes and the outcome of traffic operational analyses. At locations where existing ramp geometry to and from the general purpose lanes is proposed to be modified and requires signal control, signal timings were developed consistent with existing arterial operations and the geometry of the ramp terminals was consistent with the preliminary design concepts.

9.2.5 Other Potential Mitigation Measures After completing operational analyses of the study area intersections, additional opportunities for further mitigation were evaluated beyond those outlined in Section 9.2.4. Triggers for consideration included heightened delay as compared to the No-Build condition and sustained queue spillback from available turn lanes in excess of that expected under No-Build conditions. Heightened delay was only a consideration if LOS F was expected or the increase in delay from LOS E/F was upwards of 30 percent as compared to the No-Build condition. The majority of intersections expected to operate at LOS E in the Build condition have available capacity before triggering LOS F conditions; therefore, they were excluded from these secondary mitigation measure considerations. The following are brief summaries of the intersections with failing LOS (and the associated Build scenario) and potential mitigation measures or strategies:

US 15 and Route 55/Washington Street (2025 AM) – increased demand toward I-66 results in increased delay for the eastbound left-turn and northbound through movements. With the future construction of Express Lanes access to the west of the intersection, demand is significantly reduced in the Preferred Alternative. In lieu of specific mitigation measures, monitor operations and perform more targeted analyses as updated traffic data is available.

US 29 (Gainesville) and University Boulevard (2040 PM) – increased demand toward I-66 westbound and southbound US 29 (Gainesville) cannot be accommodated by the intersection geometry. In lieu of specific mitigation measures, it is plausible that a demand shift may occur whereby southbound trips along US 29 (Gainesville) could make use of the Bi-County Parkway to access US 29 (Gainesville) by way of I-66 westbound, which has available capacity. Monitor operations and perform more targeted analyses as updated traffic data is available. Traffic patterns could change as a result of the construction of the Bi-County Parkway, further emphasizing the need to perform focused analyses in this area.

University Boulevard and I-66 Express Lanes (2040 PM) – heavy demand from the westbound I-66 Express Lanes to access University Boulevard and adjacent land uses (e.g. park-and-ride facility, commercial properties, residential communities) results in significant queuing along the off-ramp and University Boulevard. Consider adjustments to the off-ramp geometry (exclusive left- and right-turn lanes – see Figure 9.49). Although not warranted until 2040 based on forecast demand, it is recommended that this improvement be considered in Phase 1. In addition, monitor operations and perform more targeted analyses as updated traffic data is available.



Figure 9.49: University Boulevard and I-66 Express Lanes (Phase 1 and Preferred Alternative)

University Boulevard and Wellington Road (2040 AM) – increased demand toward I-66, in part due to the Express Lanes access and planned development to the south of the intersection, which is captured in the forecast traffic demand, results in significant delays along the eastbound and southbound approaches. In lieu of specific mitigation measures, monitor operations and perform more targeted analyses as updated traffic data is available. A low-cost operational enhancement that could be considered is operation of the westbound right-turn movement with an overlap phase.

Westfields Boulevard and Park Meadow Drive (2025 PM, 2040 PM) – heavy turning volumes from this intersection towards the Route 28 interchange are expected. The volumes are heavier than originally analyzed when the MWCOG regional land uses were used for 2025 due to a subsequent approval of a rezoning on the north side of Westfields Boulevard between Park Meadow Drive and Newbrook Drive. A supplemental traffic analysis has been conducted that includes the additional rezoned land use and related traffic for the 2025 PM peak conditions, which represents the worst case conditions. The intersection of Westfields Boulevard and Park Meadow Drive is expected to operate at a poor level of service, with greater delays in Phase 1 due to greater background demand growth compared to No-Build. However, the magnitude of such increase in delays and queues is insignificant and it can be concluded that the I-66 Phase 1 alternative does not have significant impact to the traffic operations at the Route 28/Westfields Boulevard interchange and at the adjacent intersections. The Route 28 ramps and C-D roads are minimally impacted by the arterial network operations in both No-Build and Phase 1. Traffic



operations in 2040 conditions can be expected to deteriorate further with potential impacts to the Route 28 mainline.

Westfields Boulevard and Stonecroft Boulevard (2040 AM) – greater throughput from Route 28 and enhanced local access with Poplar Tree Road and Stone Road connections results in elevated traffic volumes. Consider providing an acceleration lane for the southbound right-turn movement to allow for free-flow operating conditions and construct a second northbound left-turn lane (see Figure 9.50). Both enhancements could allow for the reallocation of green time and overall reduced delay.

Figure 9.50: Westfield Boulevard and Stonecroft Boulevard

Monument Drive at I-66 Express Lanes, Government Center Parkway (2025 PM) – increased demand toward I-66 and limited intersection capacity at the Express Lanes intersection with Monument Drive results in significant delays and congestion affecting upstream intersection operations (e.g. Government Center Parkway) and queuing along the off-ramps. Consider adjustments to the off-ramp geometry from the eastbound I-66 Express Lanes (exclusive left- and right-turn lanes) in Phase 1, which would increase the capacity of the intersection, allowing for green time reallocation and overall reduced delay. In addition, consider reconfiguring the southbound approach to provide exclusive left- and right-turn lanes as well as two exclusive through lanes, which can be accomplished by reducing the number of northbound departure lanes from three to two lanes (see Figure 9.51).



Figure 9.51: Monument Drive and I-66 Express Lanes (Phase 1)

Route 123 and Eaton Place (2025 PM, 2040 AM and PM) – heavy westbound right-turn volume has limited green time allocation, in part due to clustered signal operations. Consider reconfiguring the westbound approach to Route 123 to provide two exclusive right-turn lanes and a shared through and left-turn lane by restriping one of the eastbound departure lanes as an approach lane (see Figure 9.52). This would be compatible with the allowable movements to the eastbound departure lane, all of which operate in a single travel lane.



Figure 9.52: Route 123 and Eaton Place

9.2.6 Microsimulation Summary and Recommendations

Overall I-66 Corridor The traffic analyses that are performed using microsimulation and summarized in this chapter clearly demonstrates that the I-66 corridor will operate better in the Build than the No-Build for both 2025 Phase I and 2040 Preferred Alternative. The improvements in travel times, speeds, mainline and ramp junction densities, throughput volumes, ramp queue length, and intersections delay and queue length support this statement. The consumer report tables (Tables 9.39 to 9.42) show that majority of the MOEs have significant improvement in the Build scenarios as compared to the No-Build scenarios.



Table 9.39: Overall Performance Comparison for 2025 AM No-Build and Phase 1 Alternative



Value

2025 AM Phase 1 Value

Phase 1 Performance




Minutes 64 43



Minutes 41 32



Number 3 1



Veh/hr 6,100 8,000


Average for five screenline locations taken along the corridor in the EB direction. Includes vehicular, bus transit, and rail transit riders

Persons/hr

9,900 12,000



% 9 7



% 8 11



Number 16 2



Number 1 2



Number 13 0

Notes: 1. Calculations in this table were based upon the distance between Old Tavern Road and Dulles Toll Road, approximately 36 miles

2. Five screenline locations: between US 15 and Route 234 Bypass, between Route 234 Bypass and US 29 (Centreville), between US 29 (Centreville) and US 50, between US 50 and Route 243, and between Route 243 and I-495

Better < < < < > > > > Worse



Table 9.40: Overall Performance Comparison for 2025 PM No-Build and Phase 1 Alternative



Value

2025 PM Phase I Value

Phase I Performance




Minutes 59 36



Minutes 40 32



Number 4 0



Veh/hr 5,900 8,100



Persons/hr

10,800 13,500



% 17 7



% 20 24



Number 11 0



Number 1 0



Number 15 0

Notes: 1. Calculations in this table were based upon the distance between Old Tavern Road and Dulles Toll Road, approximately 36 miles.


Better < < < < > > > > Worse



Table 9.41: Overall Performance Comparison for 2040 AM No-Build and Preferred Alternative



Value

2040 AM Pref. Alt.

Value





Minutes 90 53



Minutes 46 32



Number 5 2



Veh/hr 6,100 9,100


Average for five screenline locations taken along the corridor in the peak direction EB direction. Includes vehicular, bus transit, and rail transit riders

Persons/hr

10,700 14,300



% 21 7



% 12 17



Number 21 10



Number 3 4



Number 16 6

Note: 1. Calculations in this table were based upon the distance between Old Tavern Road and Dulles Toll Road, approximately 36 miles


Better < < < < > > > > Worse



Table 9.42: Overall Performance Comparison for 2040 PM No-Build and Preferred Alternative



Value

2040 PM Pref. Alt.

Value





Minutes 66 44



Minutes 45 32



Number 4 1



Veh/hr 6,300 8,900



Persons/hr

11,900 15,100



% 17 10



% 36 19



Number 12 6



Number 0 4



Number 16 6

Note: 1. Calculations in this table were based upon the distance between Old Tavern Road and Dulles Toll Road, approximately 36 miles


Better < < < < > > > > Worse



During the AM peak, eastbound travel in the general purpose lanes sees significant improvement in the Build scenarios, particularly from US 15 to Route 28. The Route 123 exit ramp junction and Route 243 exit ramp junction remain the two bottleneck locations in the Build scenarios. However, the Build scenarios see significantly higher throughput being processed by the corridor than the No-Build scenarios. The reverse commute bottleneck from I-66 westbound to Route 28 northbound in the No-Build scenarios is addressed in the Build. The Express Lanes in both eastbound and westbound directions operate at desirable conditions.

During the PM peak, westbound travel in the general purpose lanes shows significant improvement between I-495 and Route 28. There is still significant congestion in the westbound general purpose lanes for the Preferred Alternative which originates from US 29 (Centreville) due to the right-of-way constraints at the Manassas Battlefield National Park. However, the improvements over the No-Build scenarios are evident with westbound general purpose lane queues reaching beyond I-495 in the No-Build scenario and the much higher throughput processed by the Preferred Alternative. In the Preferred Alternative, the eastbound direction sees more congestion than the No-Build between US 50 and I-495, which can be attributed to the much higher demand on I-495 southbound general purpose lanes. This causes friction for travel from I-66 eastbound to I-495 southbound. The Express Lanes in both eastbound and westbound directions operate at desirable conditions.

The majority of the intersections, both ramp intersections and adjacent intersections in the study area, operate under improved conditions in the Build scenarios than the No-Build. Very few ramp intersections are degraded in the Build scenarios. Furthermore, the Build scenarios do not demonstrate any queue spillback onto the freeway mainline from the arterials, which does occur in the No-Build scenarios at a number of locations. The frequency of queue spillover from available turn pockets at the study intersections is also reduced in the Build scenarios during the PM peak. The AM peak sees more intersections with queue spillover compared to the Preferred Alternative due to the demand constraint at the Route 28 interchange in the 2040 AM No-Build scenario.

The following section summarizes the areas of operations in general purpose lanes and at intersections that show degradation in the Preferred Alternative scenario as compared to the No-Build scenario.

AM Peak

During the AM representative hour between US 29 (Centreville) and US 50, average general purpose travel times in the eastbound direction (peak) for the Preferred Alternative are approximately 19 minutes. This represents an increase of approximately 3 minutes compared to the No-Build conditions.

During the AM representative hour in the eastbound direction (peak) at the Route 123 interchange and between Route 28 and US 50, average mainline densities for the Preferred Alternative are worse than the No-Build conditions.

The aforementioned degradation in travel time and mainline densities along the eastbound general purpose lanes can be attributed to the higher demand released by the improved Route 28/I-66 interchange in the Preferred Alternative as well as the constraint at Route 123 and Route 243.

During the AM representative hour, the following intersections in the Preferred Alternative are degraded as compared to 2040 No-Build and operate at LOS E or worse. The intersection of Route 234 Business at the I-66 EB ramps is at an interchange, but queuing from this intersection does not affect freeway mainline traffic operations. The degradation mainly results from the increased demand and throughput in the Preferred Alternative scenario at these intersections, which are mostly on primary arterials.



- University Boulevard/Wellington Road - US 50/Waples Mill Road - Route 123/Jermantown Road - Route 123/Rose Forest Drive/White Granite Road - Route 123/Eaton Place/Oak Place - US 29 (Centreville)/Old Centreville Road/Braddock Road - Westfields Boulevard/Stonecroft Boulevard - Route 234 Bypass SB Ramps/Balls Ford Road - Route 234 Business/I-66 EB Ramps

PM Peak

During the PM representative hour in the westbound direction (peak) between Route 28 and US 29 (Centreville), average travel times and mainline densities are degraded in the Preferred Alternative as compared to the No-Build scenario. This can be attributed to the fact that right-of-way constraint at Manassas Battlefield and Bull Run Park precludes widening of I-66 to have an auxiliary lane in addition to the three general purpose lanes in each direction.

During the PM representative hour in the eastbound direction, travel times and mainline densities between US 50 and I-495 for the Preferred Alternative are worse than the No-Build due to occasional queue spillback from the ramp to I-495 southbound. In 2040, capacity improvements on I-495 southbound north of I-66 allow more volume to travel south toward its interchange with US 50. In the Preferred Alternative simulations, the weave area on I-495 southbound between I-66 and US 50 would occasionally cause queues to spill back onto I-66 eastbound, resulting in slower speeds. While this congestion is not observed in the No-Build scenario, it should be noted that some traffic along I-66 eastbound in the No-Build scenario may be constrained upstream due to a bottleneck at Route 28.

During the PM representative hour, the following intersections are degraded and operate at LOS E or worse. None of these intersections are at an interchange and queuing from these intersections does not affect freeway mainline traffic operations. The degradation mainly results from the increased demand at these arterial intersections as well as the increased throughput from the freeway in the Preferred Alternative scenario.

- Westfields Boulevard/Park Meadow Drive/Newbrook Drive - US 29 (Gainesville)/University Boulevard - US 29 (Gainesville) Ramps/Linton Hall Road - Route 234 Bypass NB Ramps/Balls Ford Road - Stringfellow Road/Fair Lakes Boulevard - Route 123/Eaton Place/Oak Place - Route 123/US 50/US 29 - Route 243/US 29

Route 28 Corridor The Route 28 corridor operates better in the Build scenarios than in the No-Build scenarios under both 2025 and 2040 conditions. The scale of improved traffic operations is more profound in the southbound direction (peak) during the PM peak than in the northbound direction (peak) during the AM peak. During the PM peak, the severe congestion on southbound Route 28 is present for the entire five-hour simulation period in the 2040 No-Build scenario, which is mitigated in the Preferred Alternative to allow moderate travel speeds for the entire PM peak. The improvements are more significant than what is shown in the analyses due to the northern limit of the study area along Route 28 being at Westfield Boulevard interchange.



CHAPTER 10. SAFETY AND CRASH ANALYSIS

10.1 Introduction and Background Within the project study area from I-495 in Fairfax County to US 15 in Prince William County, I-66 is characterized by heavy congestion from commuter traffic during both the morning and evening peak periods, especially in the eastern half of the corridor. This congestion creates the potential for crashes, especially rear-end and sideswipe crashes. In addition to safety challenges caused by this congestion, sub-standard geometric features create safety impacts in the corridor. These sub-standard geometrics include short acceleration and deceleration lanes and the lack of a shoulder during peak periods. Specifically, this study identified and evaluated the current safety hot spots within the corridor and provided safety-related input throughout the roadway design process in an attempt to improve the overall level of safety in the corridor in the future.

A combination of qualitative and quantitative analyses were used to evaluate safety in the corridor. The AASHTO Highway Safety Manual (HSM) and the 2014 HSM Supplement methodologies were used to quantitatively evaluate safety throughout the study area. The predictive crash methods detailed in the HSM allow safety professionals to assist roadway designers in the quantitative evaluation of various design options. The specific HSM methodologies used for the safety analyses are described in more detail later in this chapter.

10.2 Safety Analysis Methods and Tools Traditionally, safety analysis methods have largely relied on the skill and expertise of the safety professional. In the last several years, however, model-based approaches have become prominent. The HSM provides safety professionals with a large set of methods and tools to evaluate the effectiveness of alternatives in both existing and future conditions from a safety standpoint. These methods and tools allow safety to be compared to other performance measures like traffic operations, environmental impacts, and construction costs by calculating the change in crash frequency as a function of the cross-sectional features of different alternatives.

Based on a review of the existing conditions, the study team, in cooperation with VDOT, determined that a combination of both qualitative and quantitative safety analysis methods and tools would be used to analyze the safety on mainline, ramps, and arterials in the I-66 corridor. Within this document when methods and tools are referred to as qualitative, the results are based on an evaluation of historical crash data and traffic volumes to identify crash trends and rates. When methods and tools are referred to as quantitative, the results are not only based on historical crash data and traffic volumes but also on the geometric features of the roadway. Whether qualitative or quantitative methods and tools were used depended on the required level of detail for the safety analyses and the type of data that was available for the analyses.

10.2.1 Qualitative Safety Analysis Methods and Tools The qualitative safety analysis tools relied solely on the latest available 3 years of crash and traffic data. These methods and tools consisted of:

Crash density and severity histograms (developed for the mainline). Crash heat maps for various crash types (developed for the mainline and arterials). Crash density maps (developed for the arterials). Crash rates (fatal, injury, property damage only (PDO), and total) (developed for the mainline).



Equivalent property damage only (EPDO) crashes (developed for the ramps)

These figures, maps, charts, and rates were developed for I-66 from inside I-495 at the Dulles Toll Road to Fauquier County at Old Tavern Road and along I-495 from Route 123 to US 50, summarized in half-mile segments. Additional information on the results of this qualitative analysis is provided later in this chapter.

10.2.2 Quantitative Safety Analysis Methods and Tools Highway safety and design professionals use the HSM as a resource to inform project development, design, and decision making so that resources can be allocated towards design features with the greatest potential to benefit safety and not purely for the sake of meeting design standards. The crash prediction methods identified in the HSM use, as basic input, geometric data key to roadway design and traffic data that are fundamental to project development. These safety analysis tools allow for the evaluation of existing conditions and the comparison of potential alternatives. They permit safety professionals to predict the number of crashes on the facility based on the roadway geometric features similar to how the Highway Capacity Software is used to predict how a facility will function from an operations standpoint. Safety measures can now be used, along with other design considerations such as level of service, right-of-way, environmental impacts, and cost, as a quantified evaluation factor for design-related decisions and for balancing trade-offs between evaluation criteria.

Several quantitative analysis tools exist for use in applying the HSM Part C Predictive Methods. The quantitative analysis tools use a combination of historical crash data and detailed geometric features of the roadway. For the purposes of alternatives analysis on the I-66 corridor, a combination of two quantitative tools were employed.

Enhanced Interchange Safety Analysis Tool (ISATe). ISATe is a safety analysis tool used to evaluate freeway and interchange systems. ISATe predicts crashes by crash location, i.e., mainline freeway segments, ramp segments, and ramp terminals. Inputs to the tool include both geometric and operational characteristics of roadway and ramp facilities. ISATe also analyzes ramp terminal crossroad intersections based on the number of lanes and arrangement of lanes and type of traffic control. For the purposes of mainline and interchange safety analysis on the I-66 corridor, the ISATe was used to evaluate the existing (2011), 2040 No-Build, and 2040 Build Alternatives, and 2040 Preferred Build Alternative safety conditions.

Extended HSM Spreadsheets. Extended HSM Spreadsheets represent the methods of safety analysis of roadway segments and intersections for Rural Two-Lane, Two-Way Roads (HSM Chapter 10); Rural Multilane Highways (HSM Chapter 11); and Urban and Suburban Arterials (HSM Chapter 12). The tool predicts crashes by roadway segment and intersection.

The HSM methodologies also predict crash severity for each crash type using the KABCO scale (K – fatal crashes; A, B, C – injury crashes of decreasing severity; O – Property Damage Only (PDO) crashes), in some cases crashes are also predicted by single vehicle and multiple vehicle crash types.

The safety analysis tools use crash prediction methods outlined in Part C Predictive Methods (Volume 2) of the HSM. HSM safety prediction relies on safety performance functions (SPF), which express the predicted crash frequency for a basic roadway element (i.e., freeway or ramp segment, roadway segment, or intersection) defined by a specific volume, set of base geometric conditions, and in the case of intersections, traffic control conditions. Crash modification factors (CMF) express the relative change in crash frequency that could be expected with a change in one of the base geometric or traffic control



conditions for the alternative being analyzed. The use of these predictive models supplements the calculation of crash rates and crash densities as a safety analysis approach.

HSM Part C predictive methods estimate the long-term crash frequency of the existing conditions or for proposed alternative(s). The first step in the predictive safety analysis process is predicting the number of crashes that will occur at a location based on the SPFs and CMFs. The incorporation of historical crash data, when available, is the second step in the predictive safety analysis process, resulting in the expected crash frequency. This process is known as the Empirical Bayes (EB) method. The expected crash frequency is the estimate of long-term average crash frequency of a segment, intersection, or network under a given set of geometric conditions and traffic volumes (e.g., Average Annual Daily Traffic (AADT)). If the expected crash frequency is greater than the predicted crash frequency, the crash location has the potential for safety improvement (PSI) or an expected excess average crash frequency.

If reported crash data are either not available or not applicable, then the EB Method is not used. This will be the case in situations where traffic volume, traffic control type, or geometric configuration at a site changes significantly over time so the historical crash data would no longer adequately represent the proposed condition. In this situation, an estimate of expected average crash frequency will not be calculated, so the evaluation of a safety condition would be limited to the evaluation of the estimate of predicted average crash frequency using the predictive crash models.

To be used most effectively, quantitative safety analysis tools require calibration on a state-by-state basis to accurately represent the number of crashes that can be reasonably expected on a roadway corridor. However, even lacking such calibration, the HSM tools can be used for relative evaluation of the predicted-to-expected crash frequency for existing conditions and also for comparisons between the predicted crash frequencies of design alternatives. Uncalibrated safety models were used to analyze safety in the I-66 corridor; calibration factors are not yet available for Virginia roadways. Therefore, a comparative approach using uncalibrated results was used to assess design alternatives from a safety perspective.

On I-66, a combination of computed predicted (based on crash prediction model output) and expected (combination of crash prediction model output and historical crash data) crash frequencies were used to evaluate safety in the corridor. Since existing crash data was available throughout the corridor, both predicted and expected crashes were used to compute the PSI for segments in the corridor. A summary of the different analysis tools and scenarios described above is shown in Table 10.1.

Table 10.1: Quantitative Safety Analysis Summary

2011 Existing 2040 No-Build 2040 Alternatives

2A / 2B 2040 Preferred

Build Alternative

Network Component

Freeway Arterial Freeway Arterial Freeway Arterial Freeway Arterial

Tool ISATe HSM

Spreadsheet ISATe

HSM Spreadsheet

ISATe HSM

Spreadsheet ISATe

HSM Spreadsheet

Analysis Completed?

Yes Yes Yes Yes Yes No Yes Yes

Measure(s) of

Effectiveness (MOEs)

PSI and Predicted Crashes

PSI and Predicted Crashes

Predicted Crashes

Predicted Crashes

Predicted Crashes

N/A Predicted Crashes

Predicted Crashes



10.3 Safety Analysis Areas and Zones The HSM crash prediction methods estimate the frequency of crashes for a given time period, traffic volume, and geometric conditions. For this reason, the area to be studied needs to be divided into unique segments within which the site characteristics, such as traffic volume, traffic control, and geometry, are constant. For the purposes of the guiding the quantitative safety analyses and corresponding safety data collection, two levels of segmentation were applied to define the area for safety analysis: safety analysis zones and ISATe analysis segments.

The first level segmentation used a combination of the existing design condition and future interchange design alternatives to define larger study areas centered on the major interchanges along the corridor. The largest footprint of the interchange design alternatives was used to establish the limits of the safety analysis zones on both the mainline and the arterials. By establishing these analysis limits, the study team was able to compare the existing and future design alternatives using common limits. Exhibits 10.1a and 10.1b summarize the I-66 and I-495 safety analysis zones for the quantitative safety analysis.

For the mainline I-66 segments, the boundary of each safety analysis zone was limited to approximately 1,500 feet beyond the end of the longest acceleration or deceleration lane at each interchange. Using the 1,500-foot threshold, if the safety analysis zone at successive interchanges overlapped, then the safety analysis zone was extended until there were no additional overlap areas. For the arterial segments, the length of each safety analysis zone was limited to the one adjacent intersection on the arterial beyond the existing or proposed ramp tie-in point, whichever one was farther away from I-66. Once the next adjacent intersection was determined, the safety analysis zone was extended to the end of the longest turn lane on each approach to the intersection.

Once these safety analysis zones were determined and approved, a second level of segmentation was applied to define the ISATe analysis segments within which the site conditions (geometric and traffic volume) were constant. Given the need to collect data in the corridor for the existing and future conditions in a consistent manner, the study team established a segmentation approach that required the least level of effort for data collection while also producing results that allowed for an intuitive comparison between existing and future safety conditions. Segmentation can be a very complex process when considering a combination of existing conditions and proposed alternatives, because the geometric conditions can vary greatly between existing conditions and multiple proposed alternatives.

Since the ISATe analysis was based on roadway design files for each alternative, analysis segments were defined using the design plan stationing, which were at small enough increments that the roadway cross section remained constant. Each ISATe analysis segment was set at approximately 500 feet, which also corresponded to the minimum recommended segmentation length for safety analysis in the HSM. In isolated locations, the segment lengths were increased or decreased to adjust for situations where geometric conditions could not be adequately modeled without adjustment. This segmentation approach allowed for an automated process, which simplified the data collection process, and streamlined the extraction of results for the ISATe segments and safety analysis zones.

10.4 Safety Data Collection Safety data was collected for both the qualitative and quantitative safety analyses. The data needs for these two types of safety analyses vary depending on the tools used and the timeframe of the analysis.



10.4.1 Crash Data For both the qualitative and quantitative safety analyses, 3 years of historical interstate crash data – from January 1, 2011, to December 31, 2013 – was obtained from VDOT for 36.9 miles of I-66, between milepost 36.5 (approximately 3.5 miles west of the US 15 interchange) and milepost 68.0 (approximately one mile east of the Dulles Toll Road interchange), and for I-495 between milepost 46.3 (approximately one mile north of the Route 7 interchange) and milepost 51.7 (approximately 1 mile south of the Route 650 (Gallows Road) interchange). The same three years of historical arterial crash data was obtained from VDOT at each interchange within the study area. In addition to the interchange areas within the study area, crash data was collected at proposed arterial connections along the I-66 corridor, including Route 840 (University Boulevard), Route 645 (Stringfellow Road), Route 7669 (Monument Drive), and Route 6731 (Vaden Drive).

Crash data received from VDOT was sourced from the VDOT-maintained Roadway Network System (RNS) database. The crash data was supplied in a database, which was then converted to a shapefile for use in ArcGIS using the latitude and longitude of each crash, which spatially depicted all of the crash locations. Crash data was populated with milepost information, which was then used to create crash histograms along both corridors using the VDOT-published Linear Referencing System (LRS), release 14.1.

The roadway cross section on I-66 remained consistent throughout the crash analysis period. However, the I-495 Express Lanes Megaproject was completed during the crash analysis study period, which impacted the I-495 cross section and data collection in a portion of the study area. The Megaproject, which was under construction from July 2008 through November 2012, consisted of the addition of four high-occupancy toll (HOT) lanes between the I-95/I-395/I-495 interchange in Springfield and the Dulles Toll Road interchange near McLean. Construction activities for the HOT lane project impacted the crash analysis on I-66 and I-495, since a 6-mile portion of I-495 between the US 50 interchange and the Route 7 interchange was included within the study area for the I-66 safety analysis. Because of these major construction activities on I-495, only one year of crash data, 2013, was collected for the portion of the study on I-495.

In addition to I-495, construction at one other location – I-66 at the US 29 (Gainesville) interchange – impacted crash data collection, especially on the arterial street network. Since this interchange was under construction during the entirety of the analysis period, no crash data was collected on the interchange ramps or on US 29 (Gainesville).

10.4.2 Roadway Inventory Data Quantitative safety analyses require additional data that is not typically collected during the qualitative crash data collection process. In addition to AADT on each mainline segment, interchange ramp, and arterial segment in the study area, the quantitative crash analysis tool for freeways and interchanges requires the collection and use of detailed design-level factors such as:

Lane widths, in feet Shoulder widths (inside and outside), in feet Distance to barrier (freeway/ramps), in feet Median width, in feet Clear zone width, in feet Horizontal curve radius (especially on ramps), in feet Presence of shoulder rumble strips, yes or no Weaving length, in feet



Location of ramp, left-hand or right-hand Ramp entrance and exit

Roadway inventory data for the I-66 mainline facility was collected from multiple sources. VDOT provided the following roadway inventory information for the existing conditions: average annual daily traffic (AADT), horizontal curve radii, and clear zone widths. The remaining existing conditions roadway data elements were collected using Google Earth™. For proposed future conditions, roadway data was obtained from the roadway design files for the two alternatives prepared by the study team. Where specific design details for the future conditions were unknown, the study team made assumptions based on an assessment of existing conditions and preferred design standards for the design element in question.

Following the collection of the various types of data required for the qualitative and quantitative safety analyses, the analysis of this data commenced. The safety analysis process is described in Section 10.5.

10.5 Crash History and Safety Analysis Using the collected crash data described in Section 10.4, safety professionals analyzed the existing, No-Build, and Build conditions throughout the study area. As previously mentioned, both qualitative and quantitative methods were used to evaluate safety in the corridor. Detailed reporting of the results for the qualitative and quantitative analyses for the existing conditions is described in Section 10.5.1 and Section 10.5.2.

10.5.1 Qualitative Corridor Safety Analysis A summary of the crash hot-spot locations above the 95th percentile confidence interval within the corridor are shown in Table 10.2. Interstate mainline crash data is summarized via crash histograms for crashes reported between January 1, 2011, and December 31, 2013, for I-66 (eastbound and westbound) and I-495 (northbound and southbound) by crash type in half-mile segments (Exhibit 10.2a to Exhibit 10.2g), crash injury severity (TTR Appendix F - Figures F.1a to F.1g), and roadway departure (TTR Appendix F - Figures F.2a to F.2g). The 95th percentile, or critical, crash density for the I-66 and I-495 corridor, which is defined as the average crash density plus two standard deviations, was used as a threshold for determining crash hot-spot locations.

For the purposes of qualitative crash analyses, designated high-occupancy vehicle (HOV) lanes were evaluated as general purpose lanes and were not evaluated separately from the mainline lanes. The mainline crash data was used to develop crash histograms, crash density raster heat maps, and crash rates. Using ArcGIS, ramp crashes were separated from the mainline crash analysis and were independently evaluated using EPDO ratings.



Table 10.2: Interstate Mainline Crash Hot-Spot Location

(January 1, 2011, to December 31, 2013)

Description

Average Crash Density

(crashes per half-mile segment)

Critical Crash Density

(crashes per half-mile segment)

Hot-Spot Locations: Milepost(s)

(Reference Mainline Safety Analysis Zone Exit)

I-66

Eastbound 27.7 86.8 59.5 (Exit 60 – Route 123)

61.5 – 63.0 (Exit 62 – Route 243) 64.0 (Exit 64 – I-495)

Westbound 23.0 66.9 53.0 (Exit 53 – Route 28)

60.0 (Exit 60 – Route 123) 62.5 – 63.0 (Exit 62 – Route 243)

I-495

Northbound 45.3 99.6 47.0 (Exit 47 – Route 7) 49.0 (Exit 49 – I-495)

Southbound 45.3 91.6 47.0 – 47.5 (Exit 47 – Route 7)

Crash density (“heat maps”) analyses were performed for eastbound and westbound I-66 and northbound and southbound I-495 for the following crash types:

All crashes Injury crashes Dawn and dusk crashes Dark lighting crashes AM peak period crashes PM peak period crashes Off peak period crashes Fixed-object, off-road crashes Rear-end crashes Sideswipe crashes

High-frequency crash densities on I-66 and I-495 were consistently located in the vicinity of entrance and exit ramps of interchanges, with the highest frequencies between Route 28 and I-495. Table 10.3 depicts highest density hot spots on I-66 and I-495. Eastbound I-66 crash density issues were centered on the I-495 interchange at Exit 64. However, crash density was not always centered at the same mileposts at the interchange, since the hot spots were located within 0.75 miles of the center of the interchange

An example interstate crash density map is shown in Exhibit 10.3 with the remainder of the figures located in TTR Appendix F, Figures F.3 to F.12. On westbound I-66, the Route 28 interchange was the area with the highest crash density. A different crash density color gradient scale, representing the number of crashes from lower to higher density, was used on each crash density heat map, but the high-density thresholds for the worst crash density were colored red where crashes were most prevalent for each analysis type.

Historical arterial crash density analysis also was completed for all interchanges and at proposed arterial connection improvement locations on the I-66 corridor, including Route 840, Route 645, Route 7669, and Route 6731. Crash density was evaluated by direction for each divided highway, which included all



arterials except for Route 645. It cannot be determined if any particular direction was worse than the opposing direction, but it can be concluded that the crash density hot spots were centered at entrance and exit ramps on the mainline and at intersections on the arterials. An example arterial crash density map is shown in Exhibit 10.4 with the remainder of the figures located in TTR Appendix F, Figures F.13a to F.13f.

Crash rates were calculated for total crashes, injuries, and fatalities on I-66 and I-495 mainline segments and were compared to statewide crash rates for all urban interstates in Virginia. The average statewide crash rates for roadways functionally classified as Urban Interstates are lower than the crash rates computed in the I-66 and I-495 study areas, except for fatal crash rates where there is a marginal difference between the rates. Additionally, the crash rates within each safety analysis zone, developed for the qualitative crash data analysis and discussed in Section 10.4, were calculated for comparison of segments throughout the corridor. Crash rates are displayed by safety analysis zone in Exhibit 10.5a and Exhibit 10.5b. The corridor and statewide comparisons for crash rates in the study area are shown in Table 10.4. Table 10.5 summarizes crash rates for each safety analysis zone in the corridor.



Table 10.3: Interstate Mainline Crash Hot-Spot Locations by Crash Type

(January 1, 2011, to December 31, 2013)

Crash Type and Red Density Threshold

(crashes per mile)

I-66 Mainline WB Milepost

(Safety Analysis Zone Exit)

I-66 Mainline EB Milepost


I-495 Mainline NB Milepost


I-495 Mainline SB Milepost


All crashes >200 (I-66) & >180 (I-495)

53.6 (Exit 53 - Route 28)

59.6 (Exit 60 - Route 123)

64.7 (Exit 64 - I-495) 49.0 (Exit 49 - I-66) 47.4 (Exit 49 - I-66) 47.5 (Exit 49 - I-66)

Injury crashes >75 (I-66) & >60 (I-

495)

59.6 (Exit 60 - Route 123)*

62.0 (Exit 62 - Route 243)

64.7 (Exit 64 - I-495) 49.0 (Exit 49 - I-66) 47.5 (Exit 4947 -

Route 234 Business)*

Dawn and dusk crashes

>10

53.5 (Exit 53 - Route 28)

47.8 (Exit 47 - Route 234 Business) 49.0 (Exit 49 - I-66) 50.0 (Exit 50 -

US 50)*

Dark lighting crashes

>10 (I-66) & >25 (I-495)

67.5 (Exit 67 - Dulles Toll Road)*

37.1 (I-66 ML) 64.6 (Exit 64 - I-495)

47.4 (Exit 47 - Route 234 Business)*

47.5 (Exit 49 - I-66) 48.5 (I-495 ML)

AM peak crashes >50

54.7 (Exit 53 - Route 28)

48.5 (Exit 47) 64.8 (Exit 64 - I-495)

47.5 (Exit 47 - Route 234 Business) 50.0 (Exit 50)*

PM peak crashes >100 (I-66) & >75 (I-495)

53.4 (Exit 53 - Route 28)

63.0 (Exit 62 - Route 243)

60.0 (Exit 60 - Route 123) 48.9 (Exit 49 - I-66) 47.9 (I-495 Mainline)

Off-peak crashes >100

59.5 (Exit 60 - Route 123)*

62.4 (Exit 62 - Route 243)

64.6 (Exit 64 - I-495) 49.0 (Exit 49 - I-66) 47.5 (Exit 49 - I-66)*

Fixed-object, off-road crashes

>20

51.7 (Exit 52)* - US 29 (Gainesville))*

37.1 (I-66 ML) 65.1 (Exit 64 - I-495) 49.0 (Exit 49 - I-66)* 47.8 (Exit 49 - I-66)

48.5 (Exit 49 - I-66)

Rear-end crashes >150 (I-66) & >100 (I-495)

53.5 (Exit 53 - Route 28)* 64.7 (Exit 64 - I-495) 47.4 (Exit 49 - I-66)* 47.5 (Exit 49 - I-66)

Sideswipe crashes >20 (I-66) & >50 (I-

495)

63.2 (Exit 62 - Route 243)* 64.6 (Exit 64 - I-495) 49.0 (Exit 49 - I-66) 47.4 (Exit 49 - I-66)*

* Location did not meet maximum threshold but represents highest density of crashes in that direction.



Table 10.4: Interstate Crash Rate Summary

Description 2011 2012 2013

Fatal Injury All Fatal Injury All Fatal Injury All

I-66*

I-66 EB Study Area 0.0 31.2 97.7 0.2 35.6 99.2 0.0 32.7 105.9

I-66 EB Statewide 0.1 15.7 57.4 0.1 26.9 85.4 0.3 24.9 87.7

I-66 WB Study Area 0.5 29.4 83.2 0.3 23.0 73.4 0.0 25.7 91.4

I-66 WB Statewide 0.6 14.5 52.2 0.3 19.3 69.3 0.2 19.9 77.0

I-495*

I-495 NB Study Area 0.0 67.5 184.1 0.0 43.1 128.2 0.0 25.1 99.0

I-495 NB Statewide 0.0 64.6 114.6 0.1 29.1 92.2 0.1 24.7 75.4

I-495 SB Study Area 0.0 65.2 178.1 0.0 36.2 122.4 0.0 13.2 79.1

I-495 SB Statewide 0.0 54.3 95.6 0.0 20.6 66.9 0.0 15.5 53.4 * Crashes per 100 million vehicle-miles traveled.

Table 10.5: Freeway Safety Analysis Zone Crash Rate Summary

Description 2011 2012 2013

Fatal Injury All Fatal Injury All Fatal Injury All

I-66 Safety Zone*

Exit 40 (US 15) 0.0 12.9 46.7 0.0 16.0 56.1 0.0 9.5 41.3

Exit 43 (US 29) 0.0 13.1 50.3 0.0 8.5 50.7 0.0 23.1 73.4

Exit 44 (Route 234) 0.0 5.9 35.4 0.0 7.1 27.1 0.0 10.9 42.3

Exit 47 (Route 234) 1.2 27.0 89.2 0.0 32.6 93.0 0.0 15.2 65.4

Exit 52 (US 29) 0.0 53.2 113.9 0.0 37.0 87.2 0.0 42.3 105.8

Exit 53 (Route 28) 0.0 39.8 105.5 1.1 21.6 67.1 0.0 24.8 110.2

Exit 55 (Route 286) 0.9 17.3 52.0 0.9 20.0 52.2 0.0 18.6 61.4

Exit 57 (US 50) 0.0 14.9 53.5 0.0 20.9 62.8 0.0 26.4 66.5

Exit 60 (Route 123) 0.0 49.2 132.7 0.0 46.5 137.2 0.0 43.2 160.8

Exit 62 (Route 243) 0.0 49.8 144.7 0.0 59.8 138.2 0.0 73.0 230.7

Exit 64 (I-495) 0.0 55.9 163.8 0.0 33.0 122.6 0.0 26.9 107.7

Total I-66 0.2 30.3 90.5 0.2 29.3 86.1 0.0 29.2 98.7

I-495 Safety Zone*

Exit 49 (I-495) 0.0 66.3 181.0 0.0 39.6 125.2 0.00 19.0 88.8 * Crashes per 100 million vehicle-miles traveled.



Ramp crashes were analyzed separately from the interstate mainline crashes and were defined geospatially from the gore point on the mainline to the stop bar at the ramp-arterial intersection. There were a total of 632 crashes (31 percent) on the I-66 ramps and 473 crashes (30 percent) on the I-495 ramps. The ramp crashes were evaluated using an EPDO crash analysis, with crash costs obtained from the VDOT Fiscal Year 2013-2014 Highway Safety Improvement Program (HSIP) Application. This analysis process converted injury and fatal crashes to the equivalent monetary cost of property-damage-only crashes using weighting factors defined by VDOT. The resulting EPDO values ranged from 1 to 222 on I-66 and from 1 to 558 on I-495.

On I-66, the highest EPDO rating of 222 occurred at the Route 243 interchange for the westbound I-66 exit ramp to Route 6154 (Virginia Center Boulevard). The interchange is accessed from a one-lane collector-distributor (C-D) road with 2-foot outside and 8-foot inside shoulders. The ramp is characterized as a drop lane from the Route 6154 entrance ramp, which is 1,700 feet from the exit gore to the entrance gore. The ramp speed limit is 25 mph and is 900 feet from the ramp gore to the stop bar at the intersection.

On I-495, the highest EPDO rating of 558 occurred at the I-495/Route 7 interchange for the southbound I-495 C-D road to southbound I-495. The interchange is accessed from a one-lane C-D road with 4-foot outside and 12-foot inside shoulders. The ramp speed limit is 40 mph and is 4,200 feet from the exit gore to the entrance gore.

TTR Appendix F (Figures F.14a to F.14d and Tables F.1a to F.1c) includes reference maps and corresponding tables with the full results of the I-495 and I-66 ramp analyses.

10.5.2 Quantitative Corridor Safety Analysis The HSM methods for crash prediction were applied to the I-66 corridor for the mainline freeway facility using ISATe. One year (2011) out of the three years available between 2011 and 2013 was selected as basis for the safety analyses because 2011 included the most complete traffic volume dataset with fully-documented ramp and mainline AADTs from VDOT.

The first step in the safety analysis process was to predict the number of crashes occurring within each ISATe analysis zone based on the SPFs and CMFs. The next step was to calculate the expected crash frequency by incorporating historical crash data using the EB method. If the expected crash frequency was greater than the predicted crash frequency, the site had the potential for safety improvement (PSI) or an expected excess average crash frequency.

For predicted and expected crash calculations, the appropriate predictive models were used to compute the average crash frequency. A different model was used depending on the cross section or traffic control type at the location. The calculations were performed for each ISATe safety analysis zone. Existing 2011 ISATe summary results for I-66 and I-495 are shown in Exhibit 10.6 and Exhibit 10.8 for predicted crashes and PSI, respectively. Examples of the ISATe safety analysis zone areas for 2011 predicted crashes and PSI (full results are included in TTR Appendix G) can be found in Exhibit 10.7 and Exhibit 10.9, respectively.

Detailed predicted crash frequencies for existing 2011 conditions were calculated for each ISATe analysis zone as illustrated in TTR Appendix G, Figures G.1a to G.1l. Similar to the historical crash data analysis, locations with higher predicted crash values on I-66 and I-495 are primarily located at or adjacent to entrance and exit ramps at interchanges. Detailed PSI figures for existing conditions as calculated for each ISATe analysis zone are illustrated in TTR Appendix G, Figures G.2a to G.2l.



The results of the predicted and expected crash analyses were then aggregated by zones. As noted previously, the zones correspond to larger freeway segments generally centered at major interchanges within the study area. Table 10.6 and Table 10.7 summarize the results of the ISATe analysis for the I-66 project study area for the mainline safety analysis zones for predicted crashes and PSI, respectively. As previously mentioned, the study team focused on the characteristics and patterns from the KABC results; however, the results for PDO and total crashes are included in both tables for reference purposes. The existing conditions KABC crash values for the mainline safety analysis zones ranged from 7.8 to 55.6 and -2.3 to 34.1 for predicted crashes and PSI, respectively. Based on the PSI values in Table 10.7, the safety analysis zone with the highest potential for safety improvement is centered on the Route 243 (Nutley Street) interchange with the adjacent Route 123 interchange being the second highest zone.

Table 10.6: 2011 ISATe Predicted Crash Frequency Summary

Safety Analysis Zone Exit Number

Description

2011 Predicted Crash Frequency

(crashes/year)

KABC PDO Total

40 US 15 10 20.8 30.8

43 US 29 (Gainesville) 7.8 17.4 25.2

44 Route 234 Bypass 12.2 29.1 41.3

47 Route 234 Business 17.3 42.1 59.4

52 US 29 (Centreville) 9.2 21.7 30.9

53 Route 28 21.3 48.3 69.6

55 Fairfax County Parkway 29.0 66.7 95.7

57 US 50 35.7 82.5 118.2

60 Route 123 40.3 105.8 146.1

62 Route 243 39.3 100.8 140.1

64 I-66 at I-495 34.7 85.8 120.5

49 I-495 at I-66 55.6 142.5 198.1

HSM based arterial crash analysis also was completed on arterials that were impacted by the proposed Preferred Alternative. The HSM methods for crash prediction were applied to the I-66 corridor using the VDOT-approved Extended HSM Spreadsheets. The process used for analysis of arterials including assumptions is described in further detail in TTR Appendix G: Safety Assumptions Memo.

The original study area included US 29 (Gainesville), US 50, and Route 243 (Nutley Street). Safety analyses were not completed on these routes due to geometric incompatibility with the Extended HSM Spreadsheets, mostly due to the fact that the spreadsheets not applying to six-lane divided roadways. A qualitative review of these locations is documented in Section 10.6.2.3.



Table 10.7: 2011 ISATe Potential for Safety Improvement (PSI) Summary


Description

PSI (excess expected

crashes/year)

KABC PDO Total

40 US 15 -0.3 0.1 -0.2

43 US 29 (Gainesville) -0.1 -0.6 -0.7

44 Route 234 Bypass -2.1 -4.1 -6.2

47 Route 234 Business 3.4 7.1 10.5

52 US 29 (Centreville) 4.5 2.5 7.0

53 Route 28 4.2 9.7 13.9

55 Fairfax County Parkway -1.4 -13.0 -14.4

57 US 50 -2.1 -16.4 -18.5

60 Route 123 16.9 23.2 40.1

62 Route 243 34.1 54.6 88.7

64 I-66 at I-495 4.1 6.6 10.7

49 I-495 at I-66 -2.3 -22.1 -24.4

The first step in the safety analysis process was to calculate the predicted crashes within each safety analysis zone using SPFs and CMFs. Similar to the freeway saftey analyses, each arterial safety analysis zone was divided into smaller analysis areas. The safety analysis zones on each arterial were broken into intersection and segments – with smaller segments that could be related to a common and consistent set of geometric variables such as cross section. The predicted crash frequencies for existing conditions were calculated for each arterial safety analysis zone as illustrated in TTR Appendix G, Figures G.3a to G.3h. Refer to TTR Appendix G, Table G.1a and G.1b for predicted crashes by intersection and segment. Table 10.8 provides summary results of the predicted crashes for arterial safety analysis zones.

The next step in the safety analysis process was the application of the EB method by combining historical crash data with predicted to produce expected average crash frequencies for each analysis area. The existing crashes were subdivided into the same intersection and segment areas used in the predicted calculations for application in the analysis. Table 10.9 provides summary results of the HSM arterial analysis for PSI. Predicted KABC and PDO crashes can be found in Exhibit 10.10 and Exhibit 10.11, respectively. A summary figure of the corridor arterial safety analysis zones with the HSM existing conditions results for PSI KABC and PDO crashes can be seen in Exhibit 10.12 and Exhibit 10.13, respectively.



Table 10.8: 2011 Arterial HSM Predicted Crash Frequency Summary

Arterial Study Area

Segment Length (miles)

/ No. of Intersections

Predicted Crashes (model predicted

crashes/year)

KABC PDO Total

University Blvd (Exit 43) 0.6 / 2 0.8 1.1 1.9

Route 234 Bypass (Exit 44) 1.0 / 1 20.0 37.8 57.8

Route 234 Business (Exit 47) 0.1 / 1 0.7 1.4 2.1

Stringfellow Rd (Exit 55) 1.1 / 7 6.5 12.5 19.0

Monument Dr (HOV Access) 0.8 / 5 4.6 5.1 9.7

Route 123 (Exit 60) 0.6 / 6 13.6 19.6 33.2

Vaden Dr (Exit 62) 0.4 / 3 1.5 2.5 4.0

Route 7 (Exit 66) 0.4 / 2 7.7 11.8 19.5

55.4 91.8 147.2

Table 10.9: 2011 Arterial HSM Potential for Safety Improvement (PSI) Summary

Arterial Study Area


/ No. of Intersections


crashes/year)

KABC PDO Total


Route 234 Bypass (Exit 44) 1.0 / 1 -8.7 -16.9 -25.6




Route 123 (Exit 60) 0.6 / 6 9.5 11.8 21.3

Vaden Dr (Exit 62) 0.4 / 3 -0.1 -0.5 -0.6

Route 7 (Exit 66) 0.4 / 2 2.0 2.9 4.9

7.7 3.0 10.7

As previously mentioned, the study team focused on the characteristics and patterns from the KABC results; however, the results for PDO and Total crashes are included in both tables for reference purposes. The KABC existing conditions crash values for the arterial safety zones range from -8.7 to 8.0 and 0.7 to 20.0 for PSI and predicted crashes, respectively. Based on the PSI values in Table 10.10, the safety analysis zone with the highest potential for safety improvement is located at Route 123. The PSI for existing conditions were calculated for each arterial analysis zone as illustrated in TTR Appendix G, Figures G.4a to G.4h.

Arterial PSI hot spots were identified from the 33 study area intersections and 27 study area segments (each arterial zone was broken into smaller segments) throughout the identified safety analysis zones, which were documented in Exhibit 10.1a and Exhibit 10.1b. Intersection hot spots are defined locations at or above the average PSI plus one standard deviation for each intersection. The results of the



intersection hot spot PSI analysis is shown in Table 10.8. There were three intersections identified with the largest potential for safety improvement on the arterial network. Two intersection PSI hot spots were identified within the Route 123 arterial safety analysis zone: Orchard Street (7.4 total excess expected crashes per year) and Fairfax Boulevard (12.9 total excess expected crashes per year). These results were anticipated due to the impact of closely spaced intersections; in this case, the spacing was less than 500 feet. The other intersection hot spot was in the Route 7 arterial safety analysis zone at Idylwood Road (6.4 total excess expected crashes per year), which is also characterized by closely spaced intersections.

Generally, the segments perform better than expected, and the average PSI was negative (-1.5 total excess expected crashes per year). For the purposes of the arterial safety analysis, hot spots were identified as the segments that performed worse than expected, so any segments with positive PSIs were identified as hot spots. The segments are of varying lengths unlike the freeway segments used in the ISATe analysis. To normalize the data for segment comparison purposes, the PSI output was divided by the corridor segment length. The summary results are shown in Table 10.11. There were two arterial safety analysis zones with segments identified, one within the University Boulevard zone at I-66 access ramps to Balls Ford Road (0.9 total excess expected crashes per year per mile), and one within the Route 234 Bypass zone at US 29 to I-66 overpass (2.3 total excess expected crashes per year per mile). These two segments were longer than most of the other segments, therefore a majority of the crashes occurring within the segment were assigned to the segment versus the intersections within the HSM spreadsheet.



Table 10.10: 2011 Arterial Potential for Safety Improvement (PSI) Intersection Hot Spots

Arterial Analysis Zone

Cross Street Signalized


crashes/year)

KABC PDO Total

University Blvd (Exit 43)

Rail Line Ct No N/A N/A N/A

Wellington Rd Yes 0.1 0.1 0.2

Route 234 Bypass (Exit 44)

Balls Ford Rd Yes -6.8 -14.5 -21.3

Route 234 Business (Exit 47)

Battleview Pkwy Yes 0.6 1.0 1.6

Stringfellow Rd (Exit 55)

Northbourne Dr Yes 1.2 2.2 3.4

Fair Lakes Pkwy Blvd Yes 0.2 0.5 0.7

Residential No 0.0 -0.1 -0.1

I-66 HOV Lanes Yes 0.3 0.5 0.8

Park and Ride Yes 0.0 0.0 0.0

Autumn Willow Dr Yes -0.2 -0.3 -0.5

Centreville Farms Rd Yes -0.2 -0.3 -0.5

Monument Dr (HOV Access)

West Ox Rd Yes 1.5 1.4 2.9

Residential Yes 0.0 0.0 0.0

Fair Lakes Pkwy Blvd Yes 1.5 1.1 2.6

I-66 Yes 0.0 0.1 0.1 Government Center

Pkwy Yes 0.1 0.1 0.2

Route 123 (Exit 60)

Jermantown Rd Yes 0.2 0.3 0.5

Rose Forest Dr Yes -0.9 -1.4 -2.3

Orchard St No 3.2 4.2 7.4

Fairfax Blvd Yes 5.9 7.0 12.9

Warwick Ave No N/A N/A N/A

Blake Ln Yes 0.2 0.3 0.5

Vaden Dr (Exit 62)

Country Creek Yes -0.1 -0.2 -0.3

Saintsbury Dr Yes 0.0 -0.1 -0.1

Saintsbury Ave No 0.0 -0.1 -0.1

Route 7 (Exit 66)

Idylwood Rd Yes 2.5 3.9 6.4

Shreve Rd/Haycock Rd Yes -0.3 -0.3 -0.6

Hot Spot (Average + 1 Standard Deviation) 2.3 3.6 5.9



Table 10.11: 2011 Arterial Potential for Safety Improvement (PSI) Segment Hot Spots

Arterial Analysis Zone

Hot Spot Description Length (miles)

PSI (excess expected crashes/year)

KABC PDO Total

PSI PSI / Mile

PSI PSI / Mile

PSI PSI / Mile


US 29 to I-66 Overpass to Rail Line Ct

0.37 0.1 0.3 0.2 0.6 0.3 0.9

I-66 Overpass to Rail Line Ct to Wellington Rd

0.21 0.0 0.0 0.0 0.0 0.0 0.0


I-66 Ramps to Balls Ford Rd 0.26 0.3 1.1 0.3 1.1 0.6 2.3

Balls Ford Rd to Railroad Overpass 0.73 -2.2 -3.0 -2.7 -3.7 -4.9 -6.7 Route 234 Business (Exit 47)

East of Battleview Pkwy 0.06 -0.1 -1.7 -0.3 -5.1 -0.4 -6.8

West of Battleview Pkwy 0.09 -0.1 -1.1 -0.2 -2.3 -0.3 -3.4


Fair Lakes Pkwy to Fair Lakes Blvd 0.30 0.0 0.0 0.1 0.3 0.1 0.3

Fair Lakes Pkwy to Park & Ride 0.14 0.0 0.0 -0.1 -0.7 -0.1 -0.7

Park and Ride to I-66 Overpass 0.15 0.0 0.0 0.0 0.0 0.0 0.0

I-66 Overpass to EB Turn Lane 0.04 0.0 0.0 0.0 0.0 0.0 0.0

EB Turn Lane to Westbrook Dr 0.07 0.0 0.0 0.0 0.0 0.0 0.0

Westbrook Dr to Centreville Farms 0.18 0.0 0.0 -0.1 -0.6 -0.1 -0.6

Centreville Farms Rd 1 0.10 0.0 0.0 -0.1 -1.0 -0.1 -1.0

Centreville Farms Rd 2 0.06 0.0 0.0 0.0 0.0 0.0 0.0 Centreville Farms Rd 2 to Autumn

Willow Dr 0.08 0.0 0.0 0.0 0.0 0.0 0.0


Polo to Fair Lakes Pkwy Blvd 0.13 0.0 0.0 0.0 0.0 0.0 0.0

Fair Lakes Blvd to Overpass 0.14 0.0 0.0 0.0 0.0 0.0 0.0

Overpass to I-66 HOV Access 0.21 0.0 0.0 0.0 0.0 0.0 0.0

I-66 HOV to Government Center 0.20 0.0 0.0 -0.1 -0.5 -0.1 -0.5

Route 123 (Exit 60)

Blake Ln to Jermantown Rd 0.18 -0.2 -1.1 -0.5 -2.7 -0.7 -3.8

Jermantown Rd to White Granite 0.17 -0.2 -1.2 -0.5 -3.0 -0.7 -4.2

Eaton Rd to Orchard St 0.11 -0.1 -0.9 -0.3 -2.6 -0.4 -3.5

Orchard St to Fairfax Rd 0.09 -0.1 -1.1 -0.2 -2.2 -0.3 -3.4

Fairfax Rd to Rite Aid 0.07 0.0 0.0 -0.1 -1.4 -0.1 -1.4

Rite Aid to Warwick Ave 0.04 0.0 0.0 -0.1 -2.2 -0.1 -2.2

Vaden Dr (Exit 62)

Virginia Center Blvd to Saintsbury Dr

0.25 0.0 0.0 -0.1 -0.4 -0.1 -0.4

Saintsbury Dr to Spague Rd 0.11 0.0 0.0 0.0 0.0 0.0 0.0

Route 7 (Exit 66)

Pimmit Dr to Full Median 0.09 -0.1 -1.1 -0.2 -2.3 -0.3 -3.4

Full Median 0.05 -0.1 -1.8 -0.3 -5.5 -0.4 -7.3

Full Median to Idylwood Rd 0.07 0.0 0.0 -0.1 -1.4 -0.1 -1.4

Dale to Chestnut Rd 0.14 0.0 0.0 0.0 0.0 0.0 0.0

Chestnut Rd to Shreve Rd 0.11 0.0 0.0 -0.1 -0.9 -0.1 -0.9

Hot Spot (Average) -0.4 -1.1 -1.5



10.6 Future Conditions Safety Evaluation In addition to being a valuable tool for assessing existing conditions, ISATe can aid in the evaluation of future safety conditions and refinement of alternative designs. The operations and design elements of a proposed freeway system or interchange design project affects safety performance. Through the use of the principle and concepts in the HSM and safety analysis tools such as the ISATe and Extended HSM Spreadsheets, the design team evaluated the impact of changes to design on safety. HSM methods and tools were used to predict the safety performance of design alternatives. The HSM was also referenced, when needed, for guidance on mitigation of design elements expected to increase either crash frequency or severity and to provide valuable information on safety countermeasures that may alleviate or reduce the severity of the impact.

10.6.1 Evaluation Approach and Process Section 10.5 summarized the results of the existing conditions evaluation and determination of potential for safety improvement at locations along the existing corridor. Additionally, the intent of the safety analysis is to provide insight into detailed design elements and aid in refining the Preferred Alternative during the design phase of project development. To address the second item, future conditions safety analysis was performed for the No-Build and proposed Build conditions.

10.6.2 2040 Safety Analyses The No-Build conditions, two Build alternatives, and the Preferred Build Alternative were evaluated using ISATe to determine the safety performance of the interstate within the study area and to provide information for safety professionals to assist roadway designers with the refinement of the two Build alternatives.

10.6.2.1 2040 No-Build The HSM methods for crash prediction were applied to the study area network for 2040 No-Build conditions on the I-66 mainline using the ISATe to calculate the predicted crash frequency. The detailed ISATe analysis results are located in TTR Appendix G, Figures G.5a to G.5l; however, a summary of these results can be found in Exhibit 10.14. A safety analysis zone area example of the ISATe No-Build results for predicted crashes in 2040 can be seen in Exhibit 10.15. Since future year crash data for the No-Build conditions was not available, only the predicted crash frequencies for No-Build conditions were calculated. These predicted crash frequencies were used to inform Build alternative development and design refinement. Table 10.12 summarizes the results of the ISATe analysis for the I-66 study area for the mainline safety analysis zones for 2040 No-Build predicted crashes. Comparison these results to the predicted crash frequency for the existing conditions indicated that the same crash patterns would be expected in the No-Build conditions. This crash frequency increase is directly related to the increase in traffic volume predicted for future conditions. In some cases, there were slight differences where No-Build conditions were expected to be different from existing due to the construction of planned projects along the corridor. The preferred future design alternative is compared against these existing and No-Build analyses later in this section.



Table 10.12: Freeway (ISATe) Predicted Crash Frequency Summary – 2040 No-Build


Description

2040 Predicted Crash Frequency

(crashes/year)

KABC PDO Total

40 US 15 23.4 53.9 77.3

43 US 29 (Gainesville) 14.2 32.0 46.2

44 Route 234 Bypass 25.9 63.0 88.9

47 Route 234 Business 35.8 94.7 130.5

52 US 29 (Centreville) 20.5 53.0 73.5

53 Route 28 41.9 110.4 152.3

55 Fairfax County Parkway 49.4 127.0 176.4

57 US 50 53.5 138.4 191.9

60 Route 123 53.6 150.7 204.3

62 Route 243 49.7 140.3 190.0

64 I-66 at I-495 37.2 94.5 131.7

49 I-495 at I-66 65.8 164.7 230.5

Extended HSM Spreadsheet crash analysis was completed on the arterial study area arterials for the 2040 No-Build conditions.

The original study area included US 29 (Gainesville), US 50, and Route 243. Safety analyses were not completed at these routes due to geometric incompatibility with the HSM Spreadsheets, specifically pertaining to the spreadsheets not applying to six-lane divided roadways. A qualitative review of these locations is documented in Section 10.6.2.3.

Table 10.13 summarizes the results of the analysis of the predicted crashes by arterial safety analysis zones (refer to Exhibits 10.1a and 10.1b) for the 2040 No-Build scenario. Monument Drive exhibited the highest amount of predicted crashes in the 2040 No-Build conditions but was shown to have net zero or negative PSI in the existing analysis. Of greater concern was Route 123, since it exhibited the second highest amount of the predicted crashes, and was also identified as the greatest area of potential improvement and concern in the existing analysis. Route 234 Bypass exhibited the greatest improvement from the existing to the 2040 No-Build and 2040 Preferred Alternative conditions, with 57.8 existing predicted crashes, 20.0 No-Build predicted crashes, and 22.1 Preferred Alternative predicted crashes. The crashes were centered at the Balls Ford Road intersection, which will be improved to a partial cloverleaf by removing left turns in the No-Build and Build conditions.



A summary figure of the arterial safety analysis zones with the 2040 No-Build conditions results for predicted KABC and PDO crashes can be found in Exhibit 10.16 and Exhibit 10.17, respectively. The predicted crash frequencies for the 2040 Build conditions were calculated for each arterial safety analysis zone as illustrated in TTR Appendix G - Figures G.6a to G.6h and detailed in Tables G.2a and G.2b.

Table 10.13: Arterial HSM 2040 No-Build Predicted Crash Frequency Summary

Arterial Study Area


/ # Intersections

Predicted Crashes

(model predicted crashes/year)

KABC PDO Total


Route 234 Bypass (Exit 44)* 1.0 / 0* 8.0 12.2 20.2




Route 123 (Exit 60) 0.6 / 6 16.9 25.6 42.5

Vaden Dr (Exit 62) 0.4 / 3 4.7 7.8 12.5

Route 7 (Exit 66) 0.4 / 2 10.3 16.0 26.3

57.3 90.0 147.3 *Route 234 Bypass at Balls Ford Road (two of four segments) was analyzed using ISATe. In the 2040 No-Build and 2040 Build conditions, the intersection was converted to a partial cloverleaf interchange.

10.6.2.2 2025 Safety Analysis The analysis in this document focuses on the comparison of the existing 2011 to 2040 No-Build and Preferred Build design alternative. Consideration was also given to the value of performing 2025 Build Alternative analysis. However, the analysis of 2025 design alternatives was not initially included with the analysis of the 2040 conditions due to the following:

At the onset of the project during the scoping phase, the analysis of safety conditions in 2025 was not considered a high priority when compared to the 2040 conditions; therefore, 2025 was not included in the scope of the project.

2025 design plans were not made available until after the 2040 No-Build and Build safety analyses were underway.

Given these reasons, prior to adding the 2025 analysis to this document, it was necessary to make a value-judgement-based decision as to whether the analysis would offer benefit and should be performed for submittal with this document.

Due to impacts of the accelerated project schedule and the associated fluid nature of the design process on this project, the safety analysis performed for this document was performed at the planning-level as opposed to a design-level analysis. While this level of analysis can be used to inform design to a limited extent, it is most effectively used to identify high-level safety hot spots as opposed to design-level safety needs identification. Given that many of the 2040 design details were in flux, assumptions were necessary in order to provide a reasonable evaluation of the expected safety performance. The design detail for the 2025 conditions was even less than 2040 at the time of analysis and is still expected be refined as part of the design-build procurement process under which this project will be let.



It is anticipated that the safety conclusions that could be drawn from 2025 Build conditions will be similar to the conclusions for the 2040 conditions. A comparison of the 2025 and 2040 AADTs on the mainline and arterials throughout the study area revealed that the AADTs on a large majority of the network were much lower in 2025. Given that one of the most influential variables on the safety performance of a facility is the AADT, it can be concluded that if the facility showed a positive impact on safety in 2040, the same would be true in 2025, since the AADT was lower in 2025. Additionally, as noted previously, there was no appreciable difference in safety performance between concepts, and detailed evaluation of individual design concepts was not deemed beneficial. Therefore it can also be concluded that the value of evaluating 2025 conditions during the alternative evaluation phase would be marginal, and the cost of conducting analysis could not be justified by that value.

Value can be added by reassessing the analysis once design concepts are finalized and detail is known. We therefore recommend that a component of the alternative evaluation process during the design-build bid phase be that the design-build team are to conduct analysis, as needed, to evaluate the difference in specific design details rather than the concepts in general. If a more detailed level of safety analysis for the entire design alternative is required, analysis should be completed after the design-build process is complete, when the 2025 Phase 1 plans are finalized.

10.6.2.3 2040 Preferred Build Alternative ISATe analyses were completed throughout the entire study area for the 2040 Preferred Build Alternative. The plan set for the Preferred Build Alternative is described in further detail in Section 9.1, which combines vetted sections of Build 2A and Build 2B (vetted in the TTR) to create the 2040 Preferred Build Alternative. Additionally, the plan sets are included in the 2040 Build ISATe graphics described later in this section of the report.

Table 10.14 summarizes the results of the ISATe analysis for the I-66 project study area for the mainline safety analysis zones for the 2040 Preferred Build Alternative and compares them to the 2011 Existing and 2040 No-Build ISATe analysis results. In all ISATe safety analysis zones the 2040 Preferred Build Alternative displayed a reduction in predicted crashes when compared to the 2040 No-Build conditions.

The existing conditions KABC predicted crash values for the mainline safety analysis zones range from -10.8 to 47.8. The safety analysis zone centered on Exit 52 (US 29 Centreville) displays the greatest estimated reduction in KABC crashes from the No-Build to Preferred Build Alternative, with an approximate 38 percent reduction in predicted crashes. The safety analysis zone centered on Exit 40 (US 15) displays the lowest estimated reduction in KABC crashes from the No-Build to Preferred Build Alternative, with an approximate 7 percent reduction in predicted crashes. The predicted crash frequencies for the 2040 Build conditions were calculated for each ISATe safety analysis zone as illustrated in TTR Appendix G, Figures G.7a to G.7l.

Exhibit 10.18 illustrates a summary of the 2040 ISATe Build results for theI-66 and I-495 safety analysis zones.

Route 28 was initially included as an arterial safety analysis zone, but this section of controlled-access roadway could not be analyzed as an arterial in the existing conditions or 2040 No-Build conditions due to geometric limitations (6-lane cross section versus the 4-lane maximum in the Extended HSM Spreadsheets). In the existing and 2040 No-Build conditions, the Route 28 study area had geometric limitations that also restricted the use of ISATe, primarily due to the presence of two at-grade intersections within the study area. However, in the Build condition, Route 28 was designed as limited-access facility from I-66 to the Westfields Boulevard interchange, so ISATe was used to analyze the



safety results on this section of roadway. The Route 28 ISATe results are documented in Table 10.14 and in Exhibit 10.19. The predicted crashes for the Route 28 arterial safety analysis zone are the lowest in the study area.

Table 10.14: Preferred Alternative Freeway (ISATe) Predicted Crash Comparison by Safety Analysis Zone

2011 Existing 2040 No-Build 2040 Build

Exit Number

Description

Predicted Crash Frequency

(crashes/year)


(crashes/year)


(crashes/year)

KABC PDO Total KABC PDO Total KABC PDO Total

40 US 15 10 20.8 30.8 23.4 53.9 77.3 21.8 44.4 66.2

43 US 29

(Gainesville) 7.8 17.4 25.2 14.2 32.0 46.2 10.8 21.5 32.3

44 Route 234

Bypass 12.2 29.1 41.3 25.9 63.0 88.9 19.1 39.7 58.9

47 Route 234 Business

17.3 42.1 59.4 35.8 94.7 130.5 25.2 54.9 80.1

52 US 29

(Centreville) 9.2 21.7 30.9 20.5 53.0 73.5 12.7 30.4 43.1

53 Route 28

(along I-66 ML) 21.3 48.3 69.6 41.9 110.4 152.3 29.4 65.7 95.1

53 I-66 (along Route 28)

-- -- -- -- -- -- 12.4 19.4 31.8

55 Fairfax County

Parkway 29 66.7 95.7 49.4 127.0 176.4 36.8 86.0 122.8

57 US 50 35.7 82.5 118.2 53.5 138.4 191.9 40.8 91.8 132.6

60 Route 123 40.3 105.8 146.1 53.6 150.7 204.3 39.9 98.0 137.8

62 Route 243 39.3 100.8 140.1 49.7 140.3 190.0 44.1 105.0 149.0

64 I-66 at I-495 34.7 85.8 120.5 37.2 94.5 131.7 33.0 75.0 108.0

49 I-495 at I-66 55.6 142.5 198.1 65.8 164.7 230.5 47.8 108.4 156.2

HSM predictive spreadsheet analyses were completed at eight locations along the I-66 and I-495 corridor. The original study area also included US 29 (Gainesville), US 50, and Route 243. However, analysis was not completed at these locations due to geometric compatibility constraints in the HSM and ISATe Spreadsheets. At these locations there were no geometric changes from the existing and No-Build conditions. Additionally, traffic volume growth was minimal or reduced in the 2040 Build conditions. Direct access to the Express Lanes is not available at these arterials, which contributes to the reduction in volume.



Table 10.15 summarizes the change in AADT from the No-Build to Build conditions. Due to the minimal or improved changes, safety impacts at these locations would be expected to operate similar to the future No-Build conditions

Table 10.15: Arterial 2040 No-Build and Preferred Build Comparison

Arterial Study Area Type of

Roadway

AADT

2040 No-Build

2040 Build % Change

US 29 (Centreville) (Exit 52) 6D 29,400 28,600 -3%

US 50 (Exit 57) 6D 24,400 21,400 -12%

Route 243 (Exit 62) 6D 17,600 18,600 6%

Table 10.16 summarizes the results of the analysis of the predicted crashes by arterial safety analysis zones (refer to Exhibit 10.1 a/b) for the Existing, 2040 No-Build, and 2040 Build scenario. Route 123 exhibits the highest amount of the predicted crashes, which was also identified as the greatest area of potential improvement and concern in the qualitative analysis. Route 234 Bypass exhibits the greatest improvement from the existing to the 2040 No-Build and 2040 Preferred Build Alternative conditions, with 57.8 existing predicted crashes, 20.0 No-Build predicated crashes, and 22.1 Preferred Build Alternative predicted crashes. The crashes are centered at the Balls Ford Road intersection, which is improved to a partial cloverleaf, removing left-turns in the No-Build and Build conditions. Exhibit 10.20 and Exhibit 10.21 illustrate the 2040 Build predicted crash frequency for the I-66 and I-495 safety analysis zones KABC and PDO predicted crashes, respectively. The predicted crash frequencies for the 2040 Build conditions were calculated for each arterial safety analysis zone as illustrated in TTR Appendix G (Figures G.8a to G.8h) and detailed in Tables G.2a and G.2b.



Table 10.16: HSM Predicted Crash Comparison by Arterial Analysis Zones

Existing (2011-2013) 2040 No-Build 2040 Build

Arterial Study Area

Seg /

Int

Predicted Crashes Seg

/ Int

Predicted Crashes Seg

/ Int

Predicted Crashes




KABC PDO Total KABC PDO Total KABC PDO Total


0.6 / 2

0.8 1.1 1.9 0.6 /

3 4.0 7.1 11.1

0.6 / 3

4.6 8.8 13.4


1.0 / 1

20.0 37.8 57.8 1.1 /

0 8.0 12.2 20.2

1.1 / 0

11.8 10.3 22.1

Route 234 Bus.(Exit 47)

0.1 /1

0.4 0.9 1.3 0.1 /1

0.7 1.3 2.0 0.1 /

1 0.7 1.3 2.0


1.1 / 7

6.5 12.5 19.0 1.1 /

7 7.1 13.1 20.2

1.1 / 7

6.3 11.9 18.2


0.8 / 5

4.6 5.1 9.7 0.8 /

5 5.6 6.9 12.5

0.8 / 5

7.7 11.0 18.7

Route 123 (Exit 60)

0.6 / 6

13.6 19.6 33.2 0.6 /

6 15.7 23.0 38.7

0.6 / 6

16.4 25.4 41.8

Vaden Dr (Exit 62)

0.4 / 3

1.5 2.5 4.0 0.4 /

3 4.7 7.8 12.5

0.4 / 4

5.0 8.1 13.1

Route 7 (Exit 66)

0.4 / 2

7.7 11.8 19.5 0.4 /

2 10.3 16.0 26.3

0.4 / 2

13.7 13.2 26.9

5.6 / 27 55.4 91.8 147.2

5.4 / 27 56.1 87.4 143.5

5.1 / 28 66.2 90.0 156.2

10.7 Future Safety Considerations – No-Build and Build Based on the results of the No-Build safety analyses conducted for this project, there are corridor-wide and interchange-specific geometric and safety deficiencies that warrant improvement in both the No-Build and Build conditions. Since the Build Alternative may not be implemented in its entirety when the first phase of construction is completed, the considerations identified in the following sections should be taken into account when design concepts are prioritized.

These safety considerations are not intended to be improvements at specific locations within the study area. Rather they are provided as key design factors impacting safety that the design teams should consider as they develop final design plans.

10.7.1 Signing and Pavement Markings Signing and pavement markings are features that must clearly communicate important messages to drivers who may be unfamiliar, distracted, or who are elderly. Both the existing and proposed design alternatives include a mixture of left- and right-hand ramps, lane drops, and widely varying interchange types, which also contribute to potential driver confusion. No direct safety performance measure allows a calculation of expected reduced crashes associated with treatments that address these types of issues;



however, there is a strong body of research that describes driver workload and relates undesirable driver behavior (unnecessary or abrupt lane changing, braking, etc.) to freeways with such features.

A project design that meets design standards must still provide crucial guidance elements where conditions defy driver expectation or present an overload of information to the driver. Positive guidance is based on the principle that the road environment is designed and operated to increase the likelihood of correct and timely responses from the user. An overall corridor signing and pavement marking plan will be an essential element of the preferred design concept and will have a significant influence on effectiveness of the design with regards to safety. An effective plan will provide sequential messages that provide appropriate prioritization clues to the driver including the spread of information into small and manageable chunks that are uniform and repetitive.

10.7.2 Design for Merging and Diverging Areas In multiple existing locations, ramp merge and diverge areas were observed as being abrupt and shorter than current design policy or are simply not the most appropriate type of terminal for the given conditions. These locations represent potential safety-based project improvements that should be considered with any design alternative. Design for acceleration and deceleration on ramps is one feature for which there is a basis for calculating a crash-reduction benefit associated with lengthening either condition. Both the current HSM as well as the ISATe include models that allow for calculation of a benefit.

10.7.3 Interchange Geometry and Configuration Design elements of interchange geometry and ramp configuration are recognized as features that influence safety performance of a freeway. Specifically, the following conditions were observed at numerous locations along I-66:

Exit ramps that are very short – even moderate queues under peak traffic may queue onto the freeway and create rear-end crashes with higher speed exiting traffic.

Weaving sections both within and between interchanges not protected by C-D roads. Left exits defy driver expectation and require special attention to mitigate for potential safety

implications of this condition.

Designing the environment in such a way that it conforms to the long-term expectancies of a driver (such as exits from a freeway always being to the right) reduces the chance of driver error and, subsequently, crashes. The HSM and the ISATe include methods for evaluating the crash-reduction benefits associated with ramp alignment, weaving segment length, ramp spacing, and ramp location (left vs. right). These tools can be used not only in this documentation to evaluate the two corridor alternatives but also as part of the design refinement and design exception review process.

10.7.4 Recurring Congestion Spikes in rear-end and sideswipe same-direction crashes were observed at several locations where no readily apparent roadway alignment, cross section, ramp design, or signing issues were observed, especially immediately west of the Route 123 interchange in the evening peak hour. Based on field reviews and traffic data, the study team concluded that such spikes were simply attributable to recurring congestion – degradation in flow downstream due to a bottleneck.

Solutions to crashes stemming from recurring congestion, short of roadway capacity improvements, include ITS and Advanced Traffic Management (ATM) systems, such as those technologies that will be



implemented in the I-66 corridor. The HSM offers evidence of the effectiveness of dynamic ‘queue ahead’ warning signs; such evidence is usable in estimating safety benefits.

The expected safety performance of freeway segments operating under recurring congestion, including number of hours of congestion, is an important metric that will be considered in the continued development of the I-66 corridor. Decisions to limit the addition of capacity are understood to create operational congestion. They should also be understood to create crash frequency and severity conditions.

10.7.5 Mainline Shoulders Sections of the I-66 corridor include hard shoulder running – allowing general traffic to use the shoulder at reduced speeds during periods of high traffic volumes. This is considered an effective method of congestion mitigation, particularly where traffic peaking is limited to a well-defined period of the day and right-of-way is limited. While the concept itself may present benefit to operations and safety, hard shoulder running also presents challenges to safety by limiting the width to enable routine enforcement and maintenance activities. The safety benefits of full shoulders include their effect on accessing a crash scene and providing necessary medical assistance. Indirect safety benefits also can be estimated based on the ability to conduct regular traffic enforcement along I-66 for drivers under the influence of alcohol, restraint use, commercial vehicle inspection, distracted driving, and speeding.

Any areas where hard shoulder running is implemented also should consider needs of enforcement. This will mean assuring that shoulders will be free of traffic during periods (evenings, weekends) when enforcement actions will be most effective and that provisions are in place for enforcement and emergency access during periods when hard shoulder running is permitted. VDOT may not conduct the enforcement, but they can provide data to the State Police and construct and maintain a freeway that enables the State Police’s enforcement activities to be conducted safely.

10.7.6 Guardrail and Barriers The field review conducted by the study team identified a mix of guardrail, barrier, walls, and end treatments. Several sections of the proposed design lack full shoulders, placing barrier closer to the edge of pavement and hence more susceptible to impacts. Impacts with guardrail that are unreported as crashes may affect its performance. Furthermore, guardrail impacts on high-speed roads generally require maintenance to repair the damage.

10.8 Safety Analysis Conclusions Planning-level crash analysis was performed using industry standard practice and highway safety analysis tools. This analysis evaluated the safety performance of the existing condition and assessed the differences between the 2040 No-Build and Build alternatives within safety analysis zones in the corridor corresponding to interchanges, freeway segments, ramp segments, intersections, and arterials affected by new ramps or access to/from the Express Lanes facility. Both qualitative and quantitative analyses were conducted to evaluate existing, No-Build, and Preferred Alternative conditions in the I-66 corridor. The safety analyses focused on the network as a system, including mainline segments, ramps, collector-distributor roads, intersections, and arterials.

The results of the safety analysis showed that the highest crash frequencies (both existing and predicted) in the study area occurred in the vicinity of the entrance and exit ramps at the interchanges along the mainline. Additionally, the magnitude of crashes was higher in the eastern side of the corridor, beginning at the US 29 (Centreville) interchange through the I-495/I-66 interchange, than the western side of the



corridor. The calculated crash rates, mainline histograms (Section 10.5.1), and ISATe existing conditions analyses (Section 10.5.2) support this conclusion. The higher crash frequencies, both existing and predicted, in the eastern portion of the corridor were attributed primarily to the higher traffic congestion and geometric restrictions.

Even with increased crash frequency, however, there was no strong indication that the severity of crashes differed along the corridor in relation to the increased frequency. While there were select areas where crash frequency peaked (hot spots), the severity was fairly consistent throughout the corridor, which can be attributed to the decreased speed associated with the congestion in the corridor. While increased crash frequency can be directly attributed to the increase in traffic volume, the relatively low speeds that are associated with congested conditions can limit and, in some cases, reduce the severity of crashes.

The quantitative ISATe safety evaluation of the mainline I-66 operations revealed an overall improvement in KABC, PDO, and total predicted crashes when the Preferred Build Alternative was compared to the 2040 No-Build conditions. The same result was true for each ISATe safety analysis zone. A significant and notable result was revealed when comparing the 2040 Preferred Build Alternative predicted crash results to the 2011 existing hot spot at the Route 123 (Exit 60) interchange – the 2040 results were lower than the existing results. This same result occurred at the I-66 at I-495 (Exit 64) interchange both on I-66 and on I-495.

The most critical safety section on I-66 under the existing conditions occurred in the 4-mile section between the Route 123, Route 243, and I-66 at I-495 safety analysis zones based on the total predicted crashes. This section of roadway is projected to operate more safely under 2040 Build conditions. The 5-mile section of I-66 between Fairfax County Parkway and Route 123 yielded the top three interchanges when comparing the difference between the 2040 No-Build and the Preferred Build Alternative predicted crashes. This section of roadway also includes the US 50 interchange.

There were a total of 5.3 miles of arterials and 29 intersections analyzed in the Preferred Build Alternative. The arterial safety analysis zone (including the safety impacts of segments and intersections) with the highest number of predicted crashes per year was Route 234 Bypass (Exit 44).

Overall, the safety conditions in the I-66 corridor under the Preferred Build Alternative operations showed improvement over the No-Build operations. The most critical safety locations will continue to be the areas with the highest traffic volume exposure between Fairfax County Parkway and I-495. As the project moves forward to detailed design when potential design exceptions are evaluated and considered, attention should be paid in the areas identified as hot spots within the future No-Build and Preferred Build Alternative as well as the future safety considerations detailed in Section 10.7. This information will be valuable in refining design elements and assessing proposed design exceptions for the potential effect on safety performance.



CHAPTER 11. LAND USE COMPATIBILITY

11.1 Current Land Use The land use (built environment) and land cover (natural environment) around I-66 are typical of a densely developed urban and suburban setting. The population and employment growth of the greater Washington, DC, region has directly influenced the land use/land cover and development of the jurisdictions adjacent to I-66: Fairfax County, the City of Fairfax, the Town of Vienna, Prince William County, the City of Manassas, the Town of Haymarket, and the City of Falls Church. The various jurisdictions include a wide variety of land uses/land covers: residential, commercial, industrial, recreation/open space, and public uses. Even though some areas of each jurisdiction are densely developed, each has been able to maintain parks/open space, preservation/environmental resources, and/or recreational areas.

This section provides summaries of the existing land use conditions within the different counties, cities, and towns included in the I-66 study area, followed by a discussion of the existing land use within the I-66 study area.

11.1.1 Fairfax County/City of Fairfax/Town of Vienna Fairfax County encompasses 399 square miles (255,360 acres). Over the past 50 years, Fairfax County has changed from a primarily rural and agricultural area to an urbanized metropolitan area. The county, particularly the eastern portion, is now largely developed and includes a mixture of low-density residential, commercial, industrial, and public land uses. Slightly more than half of the land in Fairfax County is used for residences. Industrial and commercial land uses each account for almost 4 percent of the total developed acreage. Other major land uses include parkland and public facilities. About 16 percent of the land in Fairfax County is currently vacant or undeveloped open space.

The City of Fairfax has a total land area of 6.3 square miles (4,032 acres). Land use in the city is primarily dedicated to residential, commercial, institutional and open space. The city is currently built out with vacant land constituting less than 1 percent of its total acreage. The city is located adjacent to the south side of I-66.

The Town of Vienna, located within Fairfax County, encompasses approximately 18.75 square miles (12,000 acres), or about 5 percent of the county. The town is predominantly single-family neighborhoods, with a smaller portion of land devoted to commercial and public use. Less than 1 percent of land in the Town of Vienna is currently vacant. The southern edge of the town is adjacent to and on both sides of I-66.

11.1.2 Prince William County/City of Manassas/Manassas Park/Town of Haymarket

Prince William County comprises 348 square miles (222,720 acres) and is divided into a Development Area and a Rural Area according to their present and potential character as measured through both citizen expectations and goals for future development and the county’s desire for fiscally sound growth patterns.

The Development Area is that portion of Prince William County that has already been developed or is expected to be developed at residential densities greater than those in the Rural Area. The Development



Area includes established residential, commercial, and industrial areas, as well as undeveloped or underdeveloped land expected to meet the county’s projected growth.

The Rural Area is the area of Prince William County which contains agricultural, open space, forestry, and large-lot residential land uses, as well as occasional small-scale convenience retail centers and community facilities. The purpose of the Rural Area designation is to help preserve the county’s agricultural economy and resources, the quality of the groundwater supply, and the open space and rural character presently found there.

The City of Manassas encompasses 10 square miles (4,200 acres). Land use is primarily residential with some commercial and industrial areas as well. The Manassas Regional Airport occupies the entirety of the southwestern portion of the city. The City of Manassas is almost entirely built out. The city is 2.25 miles south of I-66.

The City of Manassas Park encompasses 2.6 square miles (1,600 acres). Land use is primarily residential with some commercial areas. The city has prospects of significant future residential and commercial development. The city is 1.75 miles south of I-66.

The Town of Haymarket is located within Prince William County and covers an area of 320 acres. Slightly more than a third of the land in Haymarket is currently open or undeveloped. Of the land that is developed, a majority is residential along with smaller areas of commercial and light industrial development. The town is adjacent to both sides of I-66

11.1.3 City of Falls Church The City of Falls Church occupies about 1.7 square miles (1,076 acres). Land use in the city has remained fairly stable over the last 10 years, with distinctive commercial corridors existing along US 29 and Route 7. The remainder of the city is developed with a mix of residential uses; with low-intensity office and professional enterprises providing transition to the commercial areas. Less than 1 percent of land within the city is vacant. The city is adjacent to and on the south side of I-66 inside I-495.

11.1.4 I-66 Study Area This section provides 10 summaries describing the land use within the I-66 study area, which extends from US 15 in Prince William County (western study limit) to I-495 in Fairfax County (eastern study limit).

US 15 to US 29 (Gainesville). The section of the I-66 study area between US 15 and US 29 (Gainesville) is located in Prince William County, with the western portion of this section passing through the Town of Haymarket. This section contains a mixture of residential, commercial, and public land uses along either side of I-66.

US 29 (Gainesville) to Route 234 Bypass. The section of the I-66 study area between US 29 (Gainesville) and Route 234 Bypass is located in Prince William County. Land use within this section is a mixture of commercial and industrial development.

Route 234 Bypass to Route 234 Business. The section of the I-66 study area between Route 234 Bypass and Route 234 Business is located in Prince William County. Land use development immediately to the south of I-66 within this section is devoted primarily to industrial and commercial uses, while Manassas National Battlefield Park occupies a large portion of land on the north with parts of the park adjacent to I-66.



Route 234 Business to US 29 (Centreville). The section of the I-66 study area between Route 234 Business and US 29 (Centreville) is primarily in Prince William County but also extends into Fairfax County. On the Prince William side, commercial interests occupy the entirety of the land to the south of I-66 while the land to the north is primarily reserved for public use, a large portion of which belongs to the Manassas National Battlefield Park, parts of which are adjacent to I-66. In the Fairfax County portion of this section, a majority of the land use is public parks and open space with a mixture of medium- and low-intensity residential development southwest of the US 29 (Centreville)/I-66 interchange.

US 29 (Centreville) to Route 28. The section of the I-66 study area between US 29 (Centreville) and Route 28 is located in Fairfax County. Land use in this section is a mixture of high- and medium-intensity residential developments.

Route 28 to Fairfax County Parkway. The section of the I-66 study area between Route 28 and Fairfax County Parkway is located in Fairfax County. Medium- and low-intensity residential developments dominate the portion of this section west of Stringfellow Road. Public property, including a park-and-ride lot on the north and open space on the south are immediately west of Stringfellow Road. East of Stringfellow Road on the north is adjacent commercial development and on the south is low-density residential development.

Fairfax County Parkway to US 50. The section of the I-66 study area between Fairfax County Parkway and US 50 is located in Fairfax County within the Fairfax Center Area. Land use in this section is a mixture of residential and commercial development. The Fair Oaks Mall is located northwest of the US 50/I-66 interchange.

US 50 to Route 123. The section of the I-66 study area between US 50 and Route 123 is located in Fairfax County with a large portion of land to the southeast being within the boundaries of the City of Fairfax. Land use within this section is a mixture of commercial and residential development.

Route 123 to Route 243. The section of the I-66 study area between Route 123 and Route 243 is located in Fairfax County, with a portion of land to the southwest being within the boundaries of the City of Fairfax. This section consists of medium- and low-intensity residential development, as well as commercial and public land. The Vienna Metrorail station is located in the I-66 median immediately to the west of the Route 243 interchange.

Route 243 to I-495. The section of the I-66 study area between Route 243 and I-495 is located within Fairfax County, with the Town of Vienna on both sides of I-66 just west of Cedar Lane. The majority of land use within this section consists of medium-intensity residential and commercial developments, with a smaller area devoted to public use. The Dunn Loring Metrorail station is located in the I-66 median to the west of the Gallows Road overpass.

11.2 Land Use Plans and Future Land Use This section provides summaries of the land use plans and future land use conditions within Fairfax County and Prince William County, as well as the City of Falls Church, the City of Fairfax, the City of Manassas, the Town of Vienna, and the Town of Haymarket.



11.2.1 Fairfax County/City of Fairfax/Town of Vienna The Fairfax County Comprehensive Plan notes that the county “should have a land use pattern which increases transportation efficiency, encourages transit use, and decreases automobile dependency” (Fairfax County, 2014). The county also wishes to “concentrate most future development in mixed-use Centers and Transit Station Areas” and “concentrate the highest level of development intensity in areas of transportation advantage, i.e., the Tysons Corner Urban Center, cores of Suburban Centers, and Transit Station Areas” (Fairfax County, 2014). The comprehensive plan also notes that due to rapid growth over the past decades, the amount of available vacant land is diminishing and redevelopment in the identified areas (mixed-use centers, transit station areas, suburban centers) will be more prevalent in the future. Some of these areas are along the I-66 corridor (Centreville, the Fairfax Center Area, the Vienna Metrorail station area and Merrifield at the Dunn Loring Metrorail station), and development could intensify in these areas in the future.

In regards to transportation, the county supports “a multi-modal transportation system that provides transportation choices, reduces single-occupancy vehicle (SOV) use and improves air quality” and that would “provide high-occupancy vehicle (HOV) lanes on freeways and major arterials where substantial travel benefits can be realized,” such as I-66 (Fairfax County, 2014). The plan also supports “mass transit service in major commuter corridors,” which includes I-66. The county has identified I-66 as an “Ongoing Study” within the High Quality Transit Network in its draft Countywide Transit Network Study (CTNS). The network also includes light rail transit and bus rapid transit on Route 28, which would connect I-66 with Dulles International Airport and Loudoun County. The Final CTNS is expected to be approved in 2016. Finally, the comprehensive plan’s objectives link transportation and land use to present and future economic development within the county.

The City of Fairfax, as stated in its comprehensive plan, is built out (City of Fairfax, 2012). There is less than one percent of vacant land in the city. The comprehensive plan describes any new or future development as redevelopment of previously developed areas. There are no new developments planned, nor is there available land for any induced development. Therefore, future land use is expected to be similar to existing land use. In its Transportation Strategies, the city does support “projects that promote alternatives to single-occupant vehicles during the peak period on major transportation routes,” such as I-66 (City of Fairfax, 2012). The city also supports regional initiatives, such as “improved accessibility and capacity of the region’s interstate routes, particularly I-66” (City of Fairfax, 2012).

The Town of Vienna lies within Fairfax County and has its own comprehensive planning process. The town’s most recent comprehensive plan (2010) notes that almost 90 percent of the land use is built out (residential, commercial/industrial, or governmental/institutional). The remaining land is for recreational uses. The town has planned transitions between high-density commercial development to townhouse and multifamily zones to low-density, single-family detached homes (Town of Vienna, 2010). Development trends in the town have followed town policies to preserve and enhance the town character. The plan notes that Fairfax County has worked with the town to support its land use goals.


Prince William County is broken up into two general land use areas: the “Development Area,” where development has already happened or is expected to occur at residential densities greater than the rest of the county; and the “Rural Area,” which contains agricultural, open space, forestry, large-lot residential uses, and the Federal parks (Manassas National Battlefield Park and Prince William Forest Park). The current comprehensive plan (2012) encourages infill development of the Development Area instead of



more intense development occurring within the Rural Area. The land area surrounding I-66, other than Manassas National Battlefield Park and Conway-Robinson Memorial State Forest, is all part of the Development Area and includes regional and community employment centers, industrial employment, regional commercial centers, and some high-density suburban residential uses between Gainesville and Haymarket. At Haymarket in the Development Area, US 15 is a part of an American Byway and Journey through Hallowed Ground National Heritage Area. The title National Heritage Area is an honorary distinction designated by the US Congress and is not a formal historic designation of US 15. In the area of US 15 and I-66, the county has devoted future land use to a regional employment center.

The county acknowledges that growth will continue to occur but is positioning itself to include county-specific “Smart Growth” strategies to channel and shape growth into designated growth areas within the Development Area. The county will “direct new development to areas served by transit corridors; particularly designated centers of commerce, centers of community, and Mass Transit Nodes” (Prince William County, 2012). The county also proposes “centers of commerce at appropriate locations that promote high-density, mixed-use development near existing and planned multi-modal transit centers” (Prince William County, 2012). The county has focused specific plans on several sectors (geographic areas), including Gainesville/Haymarket. The concept for the Gainesville/Haymarket sector is similar to a town center, with more dense commerce and employment opportunities around US 29 adjacent to I-66, including access to mass transit options, transitioning to lower density commercial and residential uses to the west. Development pressures on land surrounding this area could intensify in the future based on the land uses identified by the county as compatible in the Gainesville/Haymarket sector.

The county does specifically mention this project in the comprehensive plan and wishes to “quicken the process of extending” I-66 HOV lanes to their termini (the Fauquier County line to the Fairfax County line) (Prince William County, 2010).

The City of Manassas has its own comprehensive planning process. The city is almost entirely built out, and the fundamental land use pattern is largely set. With few major undeveloped tracts remaining within the city, redevelopment will become increasingly more important. The city’s comprehensive plan emphasizes the need for redevelopment to occur “in a manner that improves connectivity” (City of Manassas, 2013). It also states that redevelopment should maintain “good regional access via railroad, highway, and/or airport,” such as I-66 (City of Manassas, 2013).

The Town of Haymarket is located within Prince William County and has its own comprehensive planning process. The town’s most recent comprehensive plan (2008) notes that development and property values have increased and that the “future of Haymarket must be adjusted from previous plans to embrace and exploit this growth” (Town of Haymarket, 2008). The town wishes to continue its “commitment to a well-balanced land use pattern” to include employment opportunities for residents and to consider the conditions for economic development, including proximity to I-66, US 15, US 29, and Route 55. The town expects expansion of residential and commercial uses within the town and the surrounding area based on the available vacant land in town, projected growth of surrounding county areas, and transportation improvements (Town of Haymarket, 2008).

11.2.3 City of Falls Church The City of Falls Church is located between Arlington and Fairfax counties and thus, in addition to their own comprehensive plan, is often indirectly affected by the land use decisions made in those two jurisdictions. As less than one percent of the land in the city is currently vacant, future land use will be fairly consistent with existing land use and any future growth will be largely focused on redevelopment opportunities. The city’s plan states that redevelopment should “incorporate the improvement of



pedestrian and vehicular access within the area” (City of Falls Church, 2005). The city also recognizes that its access to major transportation routes, including I-66, US 29, US 50 and two adjacent Metrorail stations, is an important asset to its strong business environment (City of Falls Church, 2005).

11.3 Activity Centers This section provides summaries of the activity centers identified by the various jurisdictions that are included in the I-66 study area.

11.3.1 Fairfax County/City of Fairfax/Town of Vienna As Fairfax County has evolved from a residential suburb to a multi-faceted urbanized area, concentrations of land and economic activity have developed throughout the county, mostly along major regional roadways such as I-66, I-495, I-95, Arlington Boulevard, and the Dulles Toll Road. The Fairfax County Comprehensive Plan identified six regional activity centers where increases in employment are anticipated in the future.

Centreville Suburban Area. The Centreville Suburban Area is located in the western portion of the county where Route 28, US 29, I-66 and Braddock Road converge. This has historically been a residential area, but after the pace of residential development increased dramatically in the 1980s, a spectrum of commercial services soon followed.

Dulles (Route 28 Corridor) Suburban Area. The Dulles Suburban Area is located in western Fairfax County, adjacent to the eastern and southern boundaries of the Washington Dulles International Airport. The area is traversed by two major highways: Route 28 and US 50. The vast majority of development is industrial and commercial use, with the remaining land reserved for public and residential use. Major facilities in this area include: Dulles Corner, Lafayette Business Park, Dulles Technology Park, Westfields, and Ellanor C. Lawrence Park.

Fairfax Center Suburban Area. The Fairfax Center Suburban Area is adjacent to, and west of, the US 50/I-66 interchange. It is characterized by a mixture of uses including: office space, various housing types, public facilities, and regional-, community-, and neighborhood-serving retail uses. Notable facilities include the Fairfax County Government Center development, the Fair Lakes commercial and residential mixed-use development, the West Ox Complex, and the Fair Oaks Regional Mall.

Flint Hill Suburban Area. The Flint Hill Suburban Area is located on both sides of Route 123 north of its intersection with I-66 and near the northern boundary of the City of Fairfax. The area is developed for a mixture of office, retail and residential uses. The majority of development, however, is office use. The area contains the AT&T corporate office site and the Flint Hill Office Park. Less than one percent of the land in this area is vacant.

Vienna Transit Station Area. The Vienna Transit Station Area encompasses the Vienna Transit Station, which is located in the median of I-66 immediately west of Route 243. The station is connected to parking and feeder bus service north and south of I-66 via enclosed pedestrian bridges above the highway. The area is primarily developed with medium- to low-density residential uses, although some mixed-use development is planned north and south of I-66, fronting on the west side of Route 243.

Merrifield Suburban Area. The Merrifield Suburban Area is generally located south of the I-66/I-495 interchange, is served by Dunn Loring-Merrifield Metrorail station, and has regional and local access from I-66, I-495, US 29, Arlington Boulevard, US 50, and Gallows Road. The area contains a mix of uses including office, medical facilities, hotel, residential, light industrial, and



retail. Major land uses include the Exxon-Mobil Oil office complex (owned by Exxon Mobil Foundation but future Inova medical campus to be focused on cancer research, genomics and personalized medicine), Fairview Park, and Inova Fairfax Hospital.


Prince William County identified six Centers of Commerce or activity centers. These Centers of Commerce are planned urban town centers and include a variety of activities with a regional draw. Two of these designated Centers of Commerce within Prince William County are located within the I-66 study area and include:

Innovation Center of Commerce. The Innovation Center of Commerce is located immediately east of Route 234 Bypass, south of I-66. Development is primarily devoted to public and commercial use. The area is home to the Prince William Campus of George Mason University and boasts a successful advanced technology business environment, Hylton Performing Arts Center, and Freedom Aquatic and Fitness Center.

Wellington Center of Commerce. Wellington is generally located just south of I-66 between the US 29 (Gainesville) and Route 234 Bypass interchanges. Land use in this area is almost exclusively industrial and commercial development.

11.3.3 City of Falls Church The City of Falls Church Comprehensive Plan identifies two major commercial corridors. The first is the Broad Street Corridor, which is anchored at the southeast end by the Eden Center and the Koons Ford auto dealership near East Broad Street on Wilson Boulevard, and at the west end by the Falls Plaza and West Falls Centers on West Broad Street. The second is the Washington Street Corridor, which begins at the Fairfax County line just inside of Graham Road and runs north through the downtown and terminates at the Arlington County line near the fire station.

11.4 Utilities Electrical transmission lines, electrical substations and transformers, telecommunications lines and towers, and water and sewage delivery systems are located along the I-66 corridor. Through the preliminary engineering design process, and continuing through the design-build process, the concessionaire’s design-build team has – and will continue – to design the tolling infrastructure and electrical and communications equipment in a manner that is coordinated with existing and proposed utilities and telecommunications systems.

11.5 Right-of-Way Due to roadway widening, extensive enhancements to multiple interchanges, and the option to accommodate for potential future Metrorail extension to US 29 (Gainesville), the Build Alternative requires that a number of right-of-way acquisitions be made throughout the corridor. Detailed drawings illustrating the location and extent of the various right-of-way acquisitions can be found in Appendix B. In all, 161 parcels would be impacted during Phase 1 of the project, with an additional 36 parcels affected when the remaining enhancements are implemented. Of the 36 parcels affected by the remaining enhancements in the Preferred Alternative, there are three parcels between US 29 (Gainesville) and US 15 affected due to storm water management facilities and requiring no residential relocations. Of the 197 total parcels impacted by the Build Alternative, 11 would require residential relocations.



11.6 Land Use Impacts A summary of the land use effects of the Build Alternative and No-Build Alternative for the entire length of the project is presented in this section.

11.6.1 Direct Land Use Conversions The Build Alternative will require the acquisition of additional right-of-way. The total acreage of right-of-way acquisition will be calculated as the design is refined. Table 11.1 shows the land use related effects for the Build Alternative and compared to the No-Build.

Table 11.1: Summary of Land Use Related Effects

Effect No-Build

Alternative Build Alternative

Direct Land Use Conversion (acres) 0 To be determined

as design is refined

Compatible with Existing Land Use Yes Yes

Consistent with Local Plans No Yes

Consistency with Long-Range Transportation Plans No Yes

Compatible with Other Planned Transportation Projects in Northern Virginia

Yes Yes

11.6.2 Consistency with Plans and Policies Improvements to I-66 are consistent with: Fairfax County, Prince William County, the City of Falls Church, the City of Fairfax, the City of Manassas, the Town of Vienna, and the Town of Haymarket’s comprehensive plans. Table 11.2 shows goals, objectives and policies in each of the various comprehensive plans for jurisdictions within the I-66 study area that are consistent with the Build Alternative.

Table 11.2: Consistency with Plans and Policies

Local Plan Goals, Objectives, and Policies Consistent with Build

Alternative

Fairfax County Comprehensive Plan Ensure that the roadway system provides adequate local access and capacity for through movement while reducing SOV use

City of Fairfax Comprehensive Plan Supports projects that promote alternatives to SOVs during peak periods on major transportation routes

Town of Vienna Comprehensive Plan Maintain adequate levels of transportation service by coordinating land uses with surface transportation facilities

Prince William County Comprehensive Plan

Ensure the capacity of the transportation network is sufficient to meet the demands placed upon it for both weekday and weekend conditions

City of Manassas Comprehensive Plan Improve regional transportation coordination to facilitate the efficient flow of traffic both around and into the city



Local Plan Goals, Objectives, and Policies Consistent with Build

Alternative

Town of Haymarket Comprehensive Plan Work with Prince William County and VDOT to facilitate ease of movement and provide an efficient transportation system

City of Falls Church Comprehensive Plan

Increase transportation safety and provide travelers with multiple options of travel modes

11.6.3 Potential for Induced Development The relationship between roadway improvements and induced development has at times generated debate and a variety of opinions regarding sprawl. While it is clear that highways may directly induce development under certain circumstances, this cause-and-effect relationship does not always transpire when a roadway improvement is made. While it is easy to assert that transportation improvements will have this effect, it is more difficult to predict with confidence when, where, and how much, especially in a dynamic urban/suburban metropolis such as the northern Virginia region where factors other than transportation influence residential and business location decisions.



CHAPTER 12. ENVIRONMENTAL CONDITIONS AND COMPLIANCE

12.1 Background The proposed project is currently undergoing the environmental planning process with the preparation of an Environmental Assessment (EA). It has been determined that the recent proposed scope of the project represented in the Preferred Alternative is not anticipated to result in significant environmental impacts. The Final EA is anticipated to be approved for public availability by June 2016, and a Finding of No Significant impacts (FONSI) is anticipated by the end of June 2016.

12.2 Environmental Summary This section describes the environmental consequences of the proposed project. The consequences are reported at two levels: one assuming the affected environment within the existing right-of-way, the other showing the anticipated impacts outside the existing right-of-way based on the conceptual plans. Additional consideration has been given to areas of particular sensitivity, such as social impacts, streams, and wetlands where conceptual design efforts have attempted to minimize impacts, or where additional efforts may need to be made during the final design to further minimize impacts.

Table 12.1 summarizes environmental resources and their relevance to the project. Table 12.2 quantifies the impacts within the existing and potentially required right-of-way for the proposed project based on the conceptual plans.

Table 12.1: Summary of Environmental Resources

Summary of Environmental Resources

Land Use Land use is largely residential or preserved open space (national and local parks) in the county areas and a mixture of commercial, office, and residential uses within and adjacent to the municipalities. Commercial, industrial, and office uses tend to be clustered at the highway interchanges.

Communities and Neighborhoods

The corridor is located in the Towns of Haymarket and Vienna, City of Fairfax, Fairfax County, and Prince William County. Communities adjacent to the corridor include: Gainesville, Wellington, Sudley, Bull Run, Uniontown, Centreville, Oakton, Merrifield, and Dunn Loring. Large residential neighborhoods adjacent to the corridor include: Centreville Farms, Willow Springs, Crystal Springs, Penderlan, Dixie Hill, Fairfax Farms, Fairchester, Fairfax Woods, Cobbdale, and Vienna Woods.

Population and Employment

The City of Fairfax, Fairfax County, and Prince William County have been experiencing steady growth from 1990 through 2013. Fairfax County is the most populous jurisdiction in the Commonwealth. Prince William County has experienced the highest level of growth, nearly doubling in population during that 20-year time frame. Population projections by the Weldon Cooper Center predict continued growth in all three localities. Major population growth is expected to continue in Prince William County, with a 58% increase in population predicted by 2040.




Minority and Low-income Populations

Of the 37 census tracts that abut the I-66 corridor, 18 have minority populations greater than 50 percent. An additional five tracts have percentages of minority population that are meaningfully greater than other tracts along the corridor. The median household income in the jurisdictions is over $97,000. There are no census tracts with median household income below the poverty level. The regional average for populations with limited English proficiency (LEP) is 13.9 percent. There are 23 census tracts with an LEP population greater than the regional average. There are no census tracts within the corridor with LEP populations greater than 50 percent.

Farmlands and Agricultural/ Forestal Districts

As required by the federal Farmland Protection Policy Act (FPPA), Form CPA-106, Farmland Conversion Impact Rating for Corridor Type Projects, was submitted to the Natural Resources Conservation Service (NRCS) for assistance in evaluating farmland impacts. According to NRCS, no prime or statewide important farmland exists in the project area due to the fact that the project area is committed to urban uses. There are no agricultural or forestal districts within the project area.

Air Quality The project is located in Fairfax and Prince William Counties, which have been designated by the US Environmental Protection Agency (EPA) as non-attainment for the eight-hour ozone national ambient air quality standard (NAAQS), maintenance for the annual fine particulate matter (PM2.5) NAAQS, and attainment for the carbon monoxide (CO) NAAQS. The assessment indicates that the project would meet all applicable air quality requirements of NEPA and federal and state transportation conformity regulations. As such, the project will not cause or contribute to a new violation, increase the frequency or severity of any violation, or delay timely attainment of the NAAQS established by EPA.

Noise Land uses within the project area that are subject to FHWA Noise Abatement Criteria (NAC) include residential areas, parks, active sport areas, schools, places of worship, hotels, and offices. There are 67 common noise environments (CNE) representing 7,495 noise receptor locations, consisting mostly of residential structures, along eastbound and westbound I-66. Studies indicate that noise abatement using noise barriers may be feasible and reasonable for 30 of them. Barriers evaluated for the other impacted receptors were not found to be feasible and reasonable. Additional studies will be necessary during the final design phase when more detailed design information is available.

Visual Quality Views from I-66 are dominated by the highway and adjacent trees, with many large portions of the corridor lined by existing noise barriers beyond which adjacent areas cannot be seen. There are occasional views of adjacent residential, commercial, and office buildings. Unique views from I-66 are limited to short duration views of open spaces within the Manassas National Battlefield Park and Bull Run Regional Park, and longer duration views of the distant Bull Run Mountains. Sensitive visual resources with views of I-66 include one Virginia Byway, seven public parks, and one National Rivers Inventory stream.

Public Parks, Recreation Areas, and Open Space Easements

There are 20 public parks and recreation areas within 100 feet of the existing right-of-way, including five schools with recreation facilities/play areas, as well as three trails.




Historic Properties Within the area of potential effects (APE), two properties, the Manassas National Battlefield Park and the Manassas Battlefield Historic District, are listed on the National Register of Historic Places (NRHP) and six other architectural resources or historic districts have been determined eligible or potentially eligible for the NRHP with concurrence by the Virginia Department of Historic Resources (DHR). One additional historic district (Fairfax Triangle Residential Historic District/Cedar Avenue Historic District, DHR # 151-0013) has been recommended eligible but lacks formal concurrence by DHR. Two archaeological sites have been identified and recommended as potentially eligible pending DHR concurrence, and one additional site (a cemetery) requires further investigation to determine NRHP eligibility.

Hazardous Materials A total of 270 sites/facilities with the potential for containing hazardous materials/wastes are located within 0.5 mile of I-66. The majority of the sites are either petroleum registered facilities or petroleum release sites. There is one solid waste management facility adjacent to the corridor. In addition, Fairfax County has bedrock formations that contain naturally occurring asbestos.

Streams The entire corridor is located within the Potomac-Shenandoah River major watershed, within two 8-digit hydrologic unit code (HUC) boundaries (Middle Potomac-Anacostia-Occoquan 02070010 and Middle Potomac-Catoctin 02070008) and within nine smaller 12-digit HUC boundaries. The study corridor crosses 10 named streams and various unnamed smaller tributaries.

Wetlands A wetlands delineation identified a total of approximately 45 acres of wetlands adjacent to I-66 and existing connector roadways (up to 100 feet beyond existing VDOT right-of-way) and within interchanges (up to 200 feet beyond existing VDOT right-of-way) within the project corridor. The types of wetlands found include palustrine forested, palustrine scrub shrub, and palustrine emergent, and palustrine freshwater ponds. The predominant wetland types are palustrine forested and palustrine emergent.

Water Quality The corridor traverses five impaired waters (Youngs Branch, Bull Run, Cub Run, Big Rocky Run, and Holmes Run) and tributaries to impaired waters (Accotink Creek and Little Rocky Run). Seven public groundwater wells have been identified within 500 feet of I-66. No EPA-designated sole source aquifers or public drinking water surface resource watersheds were identified within this area. Much of the project area drains into the Occoquan River Reservoir.

Coastal Zone Management Areas

Both Fairfax County and Prince William County are located within Virginia’s coastal zone.

Floodplains The three major FEMA-designated floodplains within the I-66 corridor include Bull Run, Cub Run, and Big Rocky Run.

Wild and Scenic Rivers There are no federally-listed Wild and Scenic Rivers in the corridor.

Wildlife Habitat The study corridor is primarily urban and suburban in nature with wildlife communities typical of urban environments. Large parks within the western portion of the corridor provide natural forest habitats. Aquatic habitats are present within the streams and ponds that lie along the corridor. There are no designated trout streams or anadromous fish use areas within 500 feet of I-66.




Natural Heritage Sites The Manassas Diabase Uplands Conservation Site, Cub Run Slopes Conservation Site, Ellanor C. Lawrence Park Conservation Site, Long Branch Stream Conservation Unit, Big Rocky Run Above Route 28 Stream Conservation Unit, and three natural heritage General Location Areas are located within 500 feet of I-66.

Threatened and Endangered Species

Based on the USFWS Information Planning and Conservation (IPAC) online review database, three federally listed species could potentially occur along the corridor: harperella, dwarf wedgemussel, and northern long-eared bat. Additionally, two state-listed species have the potential to occur along the corridor: wood turtle and brook floater.

Invasive Species The corridor consists of both developed/disturbed areas and natural areas. While invasive species are common within disturbed areas, they are often observed within the natural areas of Fairfax and Prince William Counties as well.

Table 12.2: Summary of Environmental Impacts

Summary of Environmental Impacts

Category Impacts

No-Build Preferred Alternative

Total Area (acres) 0 1,843 (1,696)1 (147)2

Homes Displaced 0 11

Businesses, Schools, Churches, Community Facilities

0 3

Section 4(f) Property 0 0.03 (0.00)1 (0.03)2

Historic Properties Within Area of Potential Effects

0 0

Number of Streams 0 106

Length of Streams (linear feet)

0 23,664 (19,036)1 (4,628)2

Wetlands (acres) 0 29.89 (17.36)1 (12.53)2

Floodplains (acres) 0 60.23 (59.94)1 (0.29)2

Wooded Areas 0 17.96 (77.68)1 (40.28)2



Summary of Environmental Impacts

Category Impacts

No-Build Preferred Alternative

Natural Heritage Resources (Conservation Sites and Stream Conservation Units)

0 13

Federally Listed Threatened or Endangered Species Identified by USFWS that may be Affected by the Proposed Project

0 3

Hazardous Material Sites

0 10

Naturally Occurring Asbestos (acres)

0 80.08 (79.65)1 (0.43)2

Agricultural and Forestal District Land Used (acres)

0 0

Prime and Unique Farmland (acres)

0 0

Violations of National Ambient Air Quality Standards

0 0

Noise Impacts4 500 homes Impacts would likely be within the range identified for Alternatives 2A (2,426 homes) and 2B (2,184 homes). The final design noise analysis will capture noise impacts and abatement measures based on the final design of the Preferred Alternative.

1 Within existing right-of-way. 2 Within areas of new right-of-way. This refers to additional right-of-way that would need to be acquired by VDOT to implement the project, including the new park-and-ride lots. 3 Impacts are reported for proposed right-of-way areas only. Natural resources occurring within the existing VDOT right-of-way are quantified and presented in Sections 4.10 through 4.14 of the EA. 4 Noise impacts calculated for the Build alternatives take into account the removal of existing noise barriers that would be necessary to implement the project. Replacement of these barriers is accounted for in the abatement analysis. Final decisions on noise barrier configurations would be based on updated noise analysis during final design and the opinions of affected property owners regarding the implementation of noise barriers.

For the Phase 1 Alternative, based on the conceptual plans, the impacts within the existing and potentially required right-of-way is 128.71 acres.



12.3 Findings

12.3.1 Indirect Effects Indirect effects are those that are caused by an action and are later in time or farther removed in distance but are still reasonably foreseeable. Indirect effects may include growth-inducing effects and other effects related to induced changes in the pattern of land use, population density or growth rate, and related effects on air and water and other natural systems, including ecosystems. The indirect effects analysis for the proposed project followed the process described in the NCHRP Report 466 and focused on the following key resources of concern: Socioeconomics; Environmental Justice; Land Use and Recreation; Historic Properties; and Natural Resources. An inventory of the notable features (i.e. specific valued, vulnerable or unique elements of the environment) of concern in the study area was developed and are detailed in Sections 4.2 through 4.16 of the Final EA and are summarized in Table 12.1 above.

To further the analysis, impact-causing activities of the proposed project were identified. These activities were then compared to the goals and trends identified earlier in the analysis to assess whether a potential for indirect effects exist. General types of project impact-causing activities include earthwork (clearing, excavation, and filling); landscaping, erosion control; remediation, reforestation; changes in traffic patterns; and changes in access.

Direct effects that may result from the proposed project can potentially trigger indirect effects through encroachment and alteration of the environment farther in distance or time. In addition to indirect effects that can be triggered by project encroachment, indirect effects can also occur as a result of induced changes in land-use patterns, population density or growth rate that would otherwise not be expected without implementation of a proposed project. General circumstances influencing the likelihood of induced development within a region that is undergoing urbanization include: extent and maturity of existing transportation infrastructure, location attractiveness, land availability and price, state of the regional economy, area vacancy rates, local political/regulatory conditions, and land-use controls.

Based on the analysis, it is anticipated that the proposed project would not substantially encourage or accelerate any changes in land use that are not already expected in any of the jurisdictions within the analysis area. In fact, improvements to the I-66 corridor are included in the comprehensive plans of the individual jurisdictions. Therefore, the Preferred Alternative is a part of the future condition of land use within the respective jurisdictions and changes in land use and/or population growth are not necessarily directly attributable to the proposed I-66 corridor improvements alone and are already anticipated and planned for by the jurisdictions.

Taking into consideration the impact-causing activities and direct effects identified in the analysis, an assessment as to whether the notable features identified in Table 12.1 would be indirectly affected by the Preferred Alternative was conducted. The following subjects were determined to potentially experience indirect effects from the Preferred Alternative and were thus selected to move forward to the analysis of indirect effects:

Socioeconomics and Land Use Parks, Recreation and Open Space Easements Historic Properties Water Resources Floodplains Wildlife and Threatened and Endangered Species



The final step in the analysis was to assess any consequences of an indirect effect and develop mitigation. Various indirect effects for the proposed project have been identified. While planning judgment allows for the identification of potential indirect effects, insufficient data exists to fully assess the consequences of these indirect effects. For example, while it is reasonable to predict that direct impacts to water quality may occur at stream crossings of I-66, there is not enough information to determine how far downstream such impacts would actually occur. Despite the lack of detailed data, the consequences of the indirect effects are expected to be minimal because the proposed improvements would modify an existing interstate facility in an environment that is highly developed and already influenced by highway-related pressures. In addition, indirect effects of the Preferred Alternative would be minimized with the application of avoidance, minimization and mitigation measures. These mitigation measures are summarized in Section 4.17.7 of the Final EA.

A more detailed discussion of the methodology and analysis of indirect effects is presented in the Indirect and Cumulative Effects Technical Memorandum.

12.3.2 Cumulative Effects Cumulative effects are defined as the impact on the environment which results from the incremental impact of the action when added to other past, present, and reasonably foreseeable future actions regardless of what agency (federal or non-federal) or person undertakes such other actions. Cumulative effects can result from individually minor but collectively significant actions taking place over a period of time. A more detailed discussion of the methodology and analysis of cumulative impacts is presented in the Indirect and Cumulative Effects Technical Memorandum.

Present and reasonably foreseeable future actions are listed in Table 12.3. These include transportation projects identified in the programmed improvements in the National Capital Region's 2014 CLRP as well as other development projects that are planned, under construction, or recently completed along the I-66 corridor.

Table 12.3: Present and Reasonably Foreseeable Future Actions

Present and Reasonably Foreseeable Future Actions

I-66/Vaden Drive Direct Access Ramps

Direct access ramps will connect I-66 HOV lane to Vaden Drive to provide access to Vienna Metrorail station.

A Categorical Exclusion has been completed for this project, and it will be designed and constructed as part of this I-66 Corridor Improvements project.

Diverging-Diamond Interchange on US 15 at I-66

Improvements include reconstructing the I-66 and US 15 interchange as a diverging diamond; construct new US 15 bridges over I-66; improve adjacent intersections at Heathcote Boulevard and Route 55; and construct a bicycle/pedestrian trail on the western side of US 15.

Under construction.




I-66 and Route 28 Improvements

Includes widening Route 28 to eight lanes with interchanges and also redesigning the I-66 interchange.

The environmental review for Phases I and II of this project, which would reconstruct portions of the Route 28 interchange, modify the intersections of Route 28 at Braddock Road/Walney Road and the entrance to Ellanor C. Lawrence Park, and provide additional and/or modified local movements near Poplar Tree Road and Stonecroft Boulevard, is included in this Tier 2 EA.

I-66 and US 29/Linton Hall Road Interchange Improvements

The project includes: four new bridges, US 29/Linton Hall grade-separation and traffic signal removal; a 5-foot concrete sidewalk and 10-foot shared-use path; 10 retaining walls and architectural treatments; roadway lighting and landscaping; temporary detour roads to keep traffic moving during construction. Two overpasses are being constructed: one carrying US 29 over the Norfolk Southern Railroad and one carrying Linton Hall and Gallerher Roads over the railroad and US 29. US 29 is being widened to six lanes and eliminating driveway entrances and two traffic signals between I-66 and Virginia Oaks Drive.

Construction completed and open to traffic in June 2015.

I-66 Widening from Gainesville to Haymarket

Widening of I-66 to four lanes in each direction between US 29 and US 15.

Under construction.

Route 234 Bypass Relocation at Balls Ford Road Interchange

Relocate the Route 234 Bypass and Balls Ford Road interchange.

Under study.

Fairfax County Parkway HOV Widen and upgrade to six and eight lanes between Dulles Toll Road and I-66.

Under construction.

Bi-County Parkway Construct four lanes on new location between I-66 at Route 234 Bypass (Prince William Parkway) and US 50.

Environmental studies underway.

Manassas National Battlefield Park Bypass

Construct four-lane facility and close US 29 and Route 234 through the Battlefield.

Environmental studies underway.




Novant Health Haymarket Medical Center

Construct a medical center at 15225 Heathcote Blvd, Haymarket at NW corner of I-66 and US 15.

Completed.

Developments north of Haymarket Medical Center

Dominion Valley Country Club, Regency at Dominion Valley (Active Adult Community) and Greenbriar Condo Association.

Completed.

Commercial Development west of US 15 and south of I-66

Haymarket Wal-Mart and Kohl’s. Completed.

Patriot Business Center, 11800 Brewers Spring Road

Industrial sites available adjacent to Balls Ford Road with 37 acres remaining with the potential for 630,000 square feet of building.

Under construction and available for purchase.

Dunn Loring/Mosaic Development

Dunn Loring-Merrifield Metrorail station mixed-use development on Gallows Road near Vienna.

Completed.

Metro West Development Vienna Metrorail station expansion on the south side of I-66 at US 29 and I-66 near the City of Fairfax. Single family, mixed use, and retail space at Vienna Metrorail station.

Under construction.

Past actions (road widening, high-occupancy vehicle (HOV) lanes, bus transit, ride-sharing programs and facilities, and Metrorail extension) have resulted in the conversion of forest and agricultural lands to residential, commercial and industrial uses as the population and economy of Prince William and Fairfax Counties and the City of Fairfax grew. The effects of these past actions are reflected in the present socioeconomic and environmental conditions that form the baseline for consideration of environmental effects of present and reasonably foreseeable future actions. Present and reasonably foreseeable future actions include continued residential, commercial, and industrial developments and transportation improvements to accommodate forecasted growth and relieve congestion. As indicated in Table 12.3, various development and transportation projects have either been recently completed, are under construction, or are being planned along the project corridor. These projects include mixed-use developments near the Dunn Loring and Vienna Metrorail stations; medical, commercial, and residential developments to the north and south of the US 15 and I-66 interchange; commercial and industrial development along US 29, north and south of I-66; and commercial and industrial development along Route 234 south of I-66.

Overall, adverse cumulative impacts from past, present, and future projects are anticipated under the Preferred Alternative for socioeconomics and land use (i.e. relocations), parks and recreation areas, historic properties, water resources, floodplains, wildlife and threatened and endangered species, air quality and noise. The majority of these adverse effects are largely attributable to past actions that occurred prior to the establishment of protective environmental regulations. Current regulatory requirements and planning practices are helping to avoid or minimize the contribution of present and future actions to adverse cumulative effects.



CHAPTER 13. ADDITIONAL SUPPORTING INFORMATION

13.1 Procurement Method and Funding Source The delivery method selected for the project is Design/Build-Finance-Operate-Maintain (DBFOM). As part of the Public-Private Partnership (P3), up to $600M will be funded by the Public Partners, and the Private Partners will fund the remaining amount.

13.2 Projected Construction Schedule Construction is scheduled to begin in late summer 2017, upon reaching financial close. Within 24 months following construction notice to proceed, 960 park-and-ride spaces will be provided. Signals will be removed on the Route 28 corridor within 30 months following construction notice to proceed. Phase 1 of the project is to be complete no earlier than November 2021.

13.3 Ramp Improvements Phasing The first ramp improvement will be at Route 28/Walney Road, and the Route 28/I-66 interchange will be second. The phasing of all other ramp improvements is to be determined.

13.4 Conceptual Sequence of Construction as Design-Build Project Due to the nature of the project as a design-build and a privately funded project, the ultimate sequence of construction will be developed by the Concessionaire. The Developer is required to remove all signalized intersections along the Route 28 corridor from south of I-66 to Westfields Boulevard within 30 months. In order to maintain traffic on I-66, VDOT envisions widening the corridor to the outside, shifting all of the lanes outward, and then constructing the Express Lanes to the inside.

13.5 Preliminary Signing Plan The preliminary signing plan is shown in Appendix E.

13.6 Information on Comprehensive Agreement Performance Measures, Technical Requirements, and Concept of Operations (ConOPS)

More information on the project can be found at the Virginia Public-Private Partnerships (VAP3) website:

http://www.p3virginia.org/projects/interstate-66-corridor-improvements/

http://www.p3virginia.org/projects/interstate-66-corridor-improvements/

final environmental assessment interchange …outside.transform66.org/documents...tier 2 final...

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