MassDOT Conference Template - Roundabout

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


In America, Traffic Circles Got Bigger Before Falling out of Favor in the 1950s

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600+ feet


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)


Traffic Circle Family

Traffic Circles

Rotaries

Traffic Calming Circles Roundabouts

Engineered Traffic Circles


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


Early Roundabout Design - Multilane

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Photo: Maryland SHA

Photo: Casey Bergh


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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• 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



• 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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• 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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• 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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• 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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• 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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• Miscellaneous Design

• Signing

• Striping

• Central island requirements

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• 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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• 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


Treating Bikes at Intersections

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Bend-In

Bend-Out


Protected Intersections

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2017 Innovation & Tech Transfer Exchange 30


1976 FHWA “Safety and Location Criteria for Bicycle Facilities”


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


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

[email protected]

Alek Pochowski, AICP, PESenior Engineer/Planner

Washington, D.C.

[email protected]

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Documents

MassDOT Conference Template - Roundabout