project 0-6997: develop capacity and cost benefits of super ......project 0-6997: develop capacity...

Project 0-6997: Develop Capacity and Cost Benefits of Super 2 Corridors

Marcus Brewer, Project Supervisor

94th Annual Transportation Short Course – October 13, 2020

Acknowledgements

• TTI Research Team• Marcus Brewer• Tim Barrette• Kay Fitzpatrick• David Florence• Brianne Glover• Steven Venglar

• TxDOT PMC• Wade Odell (RTI)• Matt Evans (FTW)• Andrew Holick (BRY)• Cathy Kratz (AUS)• Ana Mijares (LFK)• Rebecca Wells (ATL)• Mark Wooldridge (HOU)

Project Objectives (2-year project)1. Evaluate additional capacity and reductions in % time

following for Super 22. Determine capacity and % time following of fixed-length

Super 2 corridors, varying number, length, and spacing of passing lanes

3. Compare Super 2 to traditional 4U, 4D, and 2U+LT4. Compare incremental economic benefits of Super 2 vs

widening to four lanes.

Task 2• Super 2 / 2+1 highways are used around the

world for a range of traffic volumes• High truck volumes can still cause issues,

specifically at merge points• Effective passing lane length is significantly

longer than physical passing lane length• Operational analysis frequently done by

microsimulation • Previous research had not put a monetary

value on the use of Super 2 configurations

Identify Relevant Influences on Performance• Capacity and

percent time following

• Economic benefits

• Analysis methods and tools

Task 3

Identify Study SitesCollect Field DataProcess Field Data

Districts with Super 2s:

AustinBryan

ChildressCorpus Christi

El PasoLaredoParisPharr

San AntonioWichita Falls

Yoakum

• Site selection focused on sites with:

• Lower volume = may have recently been expanded from two lanes

• High volume = serious consideration for expansion to four lanes

• Truck volume = influences on operations

• Five sites • South and West Texas• 70-75 mph

• Field data predominantly based on tubes and digital video, plus field notes


Task 3

• Road tube volumes similar to TPP ADT counts at 3 of 5 sites

• Percent of following vehicles higher in passing lane, particularly at upstream end

• Speeds in passing lane higher than right lane, but generally by ≤ 3 mph

• At 4 of 5 sites, speeds in both lanes higher than upstream or downstream 2-lane section


Task 3

Preliminary Findings

Task 4 Simulation

• Primary purpose = analyze operational characteristics to identify relative benefits of:

• Super 2 corridors (2S)• Four-lane cross-sections (4U, 4D)• Two-lane cross-sections with auxiliary turning

lanes (2U+LT)

• VISSIM 2020• Latest lane-change distribution updates model

merging behavior at the end of passing lanes• Allowed passing on opposite direction for some

cross-sections• 24-hour simulation to provide daily data for

economic analysis in Task 5

Proposed measures:• Delay• Speeds• % time following

Simulation Corridor

• 40-mile generic rural highway corridor• 9 ADT levels (3K-19K in 2K increments)• 3 truck percentages (20, 30, 40)• 8 cross-sections

Code Cross‐Section Passing Lane Length

Number of Passing Lanes

2U 2‐lane undivided None None2U+LT 2‐lane undivided with

left‐turn lanes at highway intersections

None None

4U 4‐lane undivided None None4D 4‐lane divided None None2S‐23 Super 2 2 miles 3 passing lanes2S‐33 Super 2 3 miles 3 passing lanes2S‐26 Super 2 2 miles 6 passing lanes2S‐36 Super 2 3 miles 6 passing lanes

Length & Cross-Sections

Minimum Hourly Average Speed Results

2S-36 had best Super 2 performance2S-26 outperformed 2S-33 in every scenario

Total Network Delay Results

Performance of 2U+LT similar to 2U for ADTs < 15000, but it stabilized at higher volumes

Percent Time Spent Following

PTSF does not vary widely, particularly at lower volumes and truck percentages

Additional Findings

• 4D similar to 4U at ADT ≤ 13,000, but higher volumes susceptible to effects of trucks and turning vehicles

• Observed trends support safety research: alternatives that include Super 2 or turning lanes are often preferable to 4U

• Relative performance of Super 2 alternatives supports previous research: adding more passing lanes provides more benefit than adding length to passing lanes

Providing turning lanes may be more beneficial in operations, as well as safety, than providing passing lanes, if a choice must be made between the two

Task 5

• Baseline Scenario vs Project Scenario• Scenario choices:

• Undivided 2-lane • Super 2• Undivided 4-lane • Divided 4-lane

• Cost = project construction cost• Average cost per lane-mile calculated using historic

project cost examples for each scenario• Benefit = based on VHT savings and safety

• Value of time ($/hour)• Vehicle operating cost savings ($/hour)• Environmental benefits ($/hour)• Safety benefit (crash reduction)

• Model analysis based on Task 4 outputs

Conduct Economic Analyses

Task 5• Spreadsheet model

• Compares base (no-build) vs. project (build) scenario

• Default values• 20-year operating period• 40-mile corridor length• 2-year construction period• 3% discount rate• 2018 CY dollars

• Produces cost/mile for each benefit and cost• Calculates benefit/cost ratio (BCR) and net

present value (NPV)

Key Model Inputs:• Project Type

(cross-section)• Project Length• AADT• % Trucks

Task 5

Model Inputs:• Yellow cells =

user input• Gray cells =

default values that can be overridden

Task 5

Model Outputs:• Benefits over 20-

year project life• Discounted

project cost• BCR and NPV

Task 5

BCR Results:• Net benefits for

all at high ADT• Minimal benefit

for 4-lane at low ADT

• 2S-36 best results

Project Type

3,000 ADT 19,000 ADT

20% Trucks 40% Trucks 20% Trucks 40% Trucks 2S‐23 2.1 2.2 26.2 70.62S‐33 2.2 2.3 28.6 73.82S‐26 2.3 2.5 33.9 80.62S‐36 2.4 2.5 40.1 87.74U 0.2 0.2 6.2 13.44D 1.0 1.0 5.9 26.2

Task 5

NPV Results:• Similar trends to

BCR, though not identical

• Better NPV for 4-lane at high ADT, high truck %

Project Type

3,000 ADT 19,000 ADT

20% Trucks 40% Trucks 20% Trucks 40% Trucks 2S‐23 $42 $46 $977 $2,700

2S‐33 $45 $49 $1,072 $2,825

2S‐26 $52 $56 $1,277 $3,090

2S‐36 $55 $59 $1,517 $2,264

4U ($191) ($185) $1,271 $3,062

4D ($7) ($1) $829 $4,236 Note: values shown in millions of 2018 dollars

Summary of Findings

• Super 2s compared favorably (operationally and economically) to all alternatives; 2S-36 the best Super 2 performer

• Turning lanes provide favorable operational benefit at higher through volumes

• 4-lane alternatives provide higher speeds and lower delay at lower volumes, but are not economically favorable at those volumes

• 4-lane can offer high NPV at high volumes and truck percentages, but not necessarily BCR, compared to Super 2

Design process should consider the presence of turning vehicles, not just through vehicles, when evaluating cross-section alternatives.

Guidelines (0-6997-P1)

• Summarizes the findings and guidance from 20 years of TxDOT Super 2 research (0-4064, 0-6135, 0-6997) and related external studies

• Includes key material from RDM and MUTCD, plus references to those documents for more details

• 4 chapters• Introduction• Selection of Alternatives• Design Considerations• Traffic Control Devices

• Intended as primary source for practitioners


• Background discussion• Typical environment for Super 2s• Broad description of potential benefits

• What is a Super 2?• RDM definition: one in which a periodic passing

lane is added to a two-lane rural highway to allow passing of slower vehicles and the dispersal of traffic platoons

• Potential configurations (more flexible than 2+1)• Distinction from climbing lanes

IntroductionSelection of AlternativesDesign ConsiderationsTraffic Control Devices


• Operational measures• Volume/speed/delay/PTSF• Truck %• Terrain• Through vehicles vs. turning vehicles

• Safety measures• CMF (sourced from Clearinghouse and other

studies)• Economic measures

• Benefits (operating and time cost savings, safety, environmental)

• Construction costs• Tied to 0-6997 economic analysis and

spreadsheet tool



• Basic principles from RDM• Considerations for the designer• Design criteria• Taper lengths • Separation distance



• Cross-section configurations

• Passing lane length• Passing lane spacingIntroduction

Selection of AlternativesDesign ConsiderationsTraffic Control Devices


• Source documents:• TMUTCD• Traffic Standard Sheets TS2-1-18

and TS2-2-18 • Signing

• In passing lane• Advance signing

• Markings• Centerline• Taper transitions• Buffer between lanes in opposite

direction


Next Steps• Future research

• Further development of the BCA tool with additional project data

• Refine CMF for Super 2 (problem statement developed for consideration)

• Analysis of the 4D+LT cross-section• Proposed implementation

• Virtual workshops on BCA spreadsheet tool• Virtual workshops on Guidelines document

Questions?

Marcus Brewer

[email protected]

project 0-6997: develop capacity and cost benefits of super ......project 0-6997: develop capacity...

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