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Roundabouts and Bikes/MassDOT Roundabout Guide
2017 Innovation & Tech Transfer Exchange
Outline
• Early traffic circles
• The rise (and fall) of the rotary
• The roundabout
• Roundabout lessons learned
• MassDOT roundabout experience
• Forthcoming MassDOT Roundabout Guide
• Bicycles at roundabouts
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Columbus Circle, New York City
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Columbus Circle, New York City
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In America, Traffic Circles Got Bigger Before Falling out of Favor in the 1950s
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600+ feet
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Meanwhile, England Developed Off-Side Priority
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In the early 1990s, Roundabouts Came to America
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History of Roundabouts
1905First one-way circular
intersection
1966Roundabout “invented” in the United Kingdom
1990First roundabout in the United States
1991Maryland
launches first statewide roundabout program
2000FHWA publishes first roundabout
guide
2010Second edition of the roundabout guide
published
2020?Third edition of the roundabout guide published
2000sRapid growth in number of roundabouts built across the United States
1950sRotaries fell out of favor in the United States
(Not to Scale)
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Traffic Circle Family
Traffic Circles
Rotaries
Traffic Calming Circles Roundabouts
Engineered Traffic Circles
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Rotary vs. Roundabout
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Rotary vs. Roundabout
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Early Roundabout Design – Single Lane
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Photos: Maryland SHA
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Early Roundabout Design - Multilane
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Photo: Maryland SHA
Photo: Casey Bergh
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Early Roundabout Issues
• Size (predominantly too small)
• Splitter Islands (too short)
• Design Vehicles (not accommodated)
• Bicycles and Pedestrians (not fully accommodated)
• Too much sight distance
• Path Alignment (not understood at mulitlane roundabouts)
• Multilane roundabout striping (concentric or non-existent)
• Built for the design year (resulted in much higher crash rates than expected)
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Recent Roundabout Lessons Learned
• Phased design (build for future expansion to the inside)
• Accessible pedestrian crossings
• Long splitter islands (150 to 200 ft)
• Consider design vehicle needs (typically the largest vehicles don’t need to make all turning movements)
• Provide separation between large vehicles, bicycles, and pedestrians
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Benefits Considerations• Decreases vehicle
speeds • Enhances safety for
pedestrians• Provides aesthetic
opportunities• May improve access
management • May reduce delay and
emissions
• Accessibility for visually impaired pedestrians
• Right-of-way needs• Type of vehicle used for
the design (emergency vehicles, trucks, buses)
• Parking• Interaction with
adjacent traffic control devices
• Sight distance
Roundabouts Come to the City
• More users and activity than typically found in suburban/rural counterparts
• Typically constrained
• Necessitates tradeoffs
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Current MassDOT Experience
• Interviewed all six MassDOT districts in late January/early February
• Perception of roundabouts
• Varies amongst the districts related to the number of roundabouts in the District, and previous experience with rotaries
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Current MassDOT Experience
• Familiarity
• Districts are generally familiar with roundabouts, and all districts have at least one roundabout• Adoption of multilane roundabouts has been slower
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MassDOT District
Number of Roundabouts Comments
District 1 1
• Potential mini-‐roundabout in design• Other ideas for locations• Have historical downtown traffic circles
District 2 5 • Five constructed in the last 5 years. Two in design. Have rotaries as well
District 3 5
• Approximately 6 under construction now• Others in design, including a mini roundabout• Have done rotary-‐roundabout conversions
District 4 ~6 • Nothing under construction or in design
District 5 ~10• Several rotaries • No roundabout to rotary conversions
District 6 ~5• Have some in design/construction. About 30 rotaries. • Have applied roundabout characteristics to some rotaries
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Current MassDOT Experience
• Policy
• Generally good understanding of MassDOT policy in regards to roundabouts
• Massachusetts Highway Design Guide:
“Roundabouts can be appropriate design alternative to both stop-controlled and signal-controlled intersections. … At higher combinations of major street and minor street
volume, traffic signals become the common traffic control measure. Roundabouts should also be considered in these
situations.”
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Current MassDOT Experience
• Rotaries
• MassDOT staff mostly understand the difference between roundabouts and rotaries
• Other stakeholders mostly understand the different depending on past exposue
• The general public tends to use the terms interchangeably
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Current MassDOT Experience
• Analysis
• Most districts tend to use “SIDRA”
• Few distinguish between SIDRA software, the SIDRA standard model, and the HCM model in SIDRA software
• Life-cycle cost analysis and/or other safety analyses not often considered
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Current MassDOT Experience
• Design
• Most districts understand the principle-based design approach
• Quality of designs contingent on prior design experience
• Variety of local and national resources used
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Current MassDOT Experience
• Bicycle and Pedestrian
• More guidance needed
• More flexibility, especially in regards to accommodating bicycles
• Large Vehicles
• Choosing the appropriate design vehicle
• Truck apron design
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Current MassDOT Experience
• Miscellaneous Design
• Signing
• Striping
• Central island requirements
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Current MassDOT Experience
• Construction and Maintenance
• Good and bad examples of construction staging
• Lack of guidance on traffic management plans
• Grades and temporary signage during construction
• Pavement marking maintenance of both roundabouts and rotaries has been problematic
• Strategies for using local landscapers and/or gardeners to maintain the central island
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Current MassDOT Experience
• Guidebook desires
• Consolidated best practices
• Look up tables
• Graphics heavy
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Forthcoming MassDOT Roundabout Guide
An opportunity to leap frog current industry practice!• Pedestrian and bicycle design
• Constrained locations and mini-roundabouts
• Planning for roundabouts
• Public outreach
• Phased design
• Construction and maintenance of traffic
• Operations and safety analysis
• Rotary retrofits and application of roundabout features
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Recent Industry-Wide Bicycle Practice
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Sidewalk Level Cycle Track
Protected Intersection
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Treating Bikes at Intersections
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Bend-In
Bend-Out
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Protected Intersections
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1976 FHWA “Safety and Location Criteria for Bicycle Facilities”
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Bicycles and Roundabouts: Current Practice
• Low-volume: encourage bicycles to circulate with vehicles
• High-volume: provide separate bicycle path with bike ramps
First protected intersection!
• Give bicyclists option of either being vehicle or pedestrian
• Do not provide bike lanes within the circulatory roadway (prohibited by 2009 MUTCD)
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Expected bicycle design guidance in the MassDOT roundabout guide
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Combining Recent industry state-of-the practice with roundabout practice
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Inman Square• Known bicycle and pedestrian safety concerns at Inman Square
• Boston Cyclists Union engaged KAI to evaluate a roundabout option
• KAI and Boston Cyclists Union coordinated with the City of Cambridge
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Design PrioritiesPriority
• Identify a reasonable roundabout concept that provides a safe environment for pedestrians and bicyclists
Other Considerations
• Operates acceptably and minimizes queueing
• Avoids impacts to the Mayor Alfred E. Vellucci Community Plaza
• Considers access to and from the Inman Square Fire House
• Allows buses to go east-west/west-east on Cambridge Street and Hampshire Street, along with north-east/east-north on Springfield Street and Hampshire Street
• Allows WB-50 design vehicles to travel east-west /west-east on Cambridge Street and Hampshire Street
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The Peanutabout
Mini-‐Roundabout
Separated Bike Lanes Tradeoffs Peanutabout
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Mini-Roundabouts
• Mini-roundabouts are single-lane roundabouts with fully traversable central islands
• Approximately 15 mini-roundabouts are known to exist in the United States, but similar traffic calming circles are prevalent
• FHWA and other states and local jurisdictions are pushing to install more mini-roundabouts due to their relatively low costs and operational and safety benefits
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High-Level Roundabout Operations Analysis
• An analysis of the existing configuration and other alternatives was not completed by KAI
• Based on observed existing queue lengths, roundabout operations appear to be an improvement over existing conditions
• A more detailed operations analysis, potentially involving simulation, is necessary before advancing this concept
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High-Level Roundabout Operations Analysis
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Approach Conflicting PCE Entering PCE
Entering Bicycles (PCE)
Entering Bikes + Cars
(PCE)
Conflicting Pedestriansand Bikes
V/C Delay Queue (vehicles) Queue Length
AMCambridge EB 647 532 22 -- 379 1.05 82.8 15.8 400Hampshire NB 370 290 6 -- 98 0.40 10.3 2.0 50Cambridge WB 323 354 17 -- 161 0.48 11.8 2.6 75Springfield SB 607 -- -- 222 250 0.40 12.9 1.9 50Hampshire SB 607 496 128 -- 283 0.91 46.7 10.9 275
MiddayCambridge EB 515 488 10 -- 100 0.77 26.0 7.2 200Hampshire NB 420 334 10 -- 77 0.48 12.1 2.6 75Cambridge WB 375 359 11 -- 139 0.51 12.8 2.9 75Springfield SB 631 -- -- 123 266 0.23 9.8 0.9 25Hampshire SB 456 455 22 -- 252 0.72 22.6 6.1 175
PMCambridge EB 466 552 16 -- 173 0.86 34.2 9.7 250Hampshire NB 491 479 94 -- 95 0.74 23.2 6.5 175Cambridge WB 598 385 26 -- 362 0.72 26.1 5.9 150Springfield SB 796 -- -- 136 514 0.33 14.4 1.4 50Hampshire SB 479 395 23 -- 315 0.66 19.9 4.8 125
SaturdayCambridge EB 768 604 22 -- 191 1.23 145.2 23.6 600Hampshire NB 596 651 37 -- 179 1.14 106.3 21.2 550Cambridge WB 708 562 25 -- 303 1.14 110.9 19.3 500Springfield SB 1106 -- -- 159 430 0.48 22.9 2.5 75Hampshire SB 594 679 31 -- 341 1.26 155.0 26.9 675
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The first design
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Charrette
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Revised Design
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Summary
• Based on expected operations and concept design, a protected mini-roundabout concept is worthy of further consideration
• Provides likely safety improvements for all modes, especially bicyclists and pedestrians
• Compact urban environment limits operational and comfort benefits
• Additional study, including the potential for simulation, is necessary before advancing this concept further
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Thank you.
Conor Semler, AICPSenior Planner
Boston, Massachusetts
Alek Pochowski, AICP, PESenior Engineer/Planner
Washington, D.C.
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