Making the BU Bridge Safer and Better for All:

General Proposal

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BU Bridge Safety Alliance

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August 2023

What’s Wrong?

A. Bicycle Safety Issues

• No protected bike lanes
• Heavy turn right turn conflicts exiting the bridge
• 450 right turns / hr at Comm Ave
• 420 right turns / hr at Mem Drive
• MassDOT’s standard for signal separation is 150 / hr
• Affects pedestrian safety, too
• Rotary has dangerous weaves & blind crossings
• Shared use paths along Mem Drive are WAY too narrow for safe bike-pedestrian sharing

Leaving the bridge at Mem Drive

Current road layout for most of the bridge

What’s Wrong?

B. Pedestrian Safety Issues

• Lack of protected bike lanes means many bikes use the sidewalks
• Crossing Comm. Ave: Heavy right turn conflicts
• 450 right turns / hr turn from the bridge onto Comm Ave
• 4-second Leading Pedestrian Interval isn’t long enough for such a long crossing
• Uncoordinated crossings on the Cambridge side force people to wait twice; many just dash

Mouth of the BU Bridge at Mem Drive

What’s Wrong?

C. Massive Congestion Makes Buses Slow and Unreliable

• Average southbound bus delay ≅ 7 minutes (pm peak, entering Boston)
• Bus delay often exceeds 13 minutes (90th percentile delay)
• Impacts Routes 47, CT 2, LMA buses
• Backups often paralyze Cambridgeport streets
• Congestion also contributes to the high crash rate

What’s Wrong?

D. Too Many Crashes and Injuries

87 crashes reported between 2018-2022

• 15 bike crashes
• 2 pedestrian crashes
• Several 3- and 4-car crashes on the bridge, symptomatic of excessive congestion
• 2 autos crashed into Green Line trains in 2022
• At least 32 persons injured
• 55 crashes in the rotary

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See Crash Data folder for more details

Crash map. Large yellow circles are crashes with 3+ parties. While map includes crashes on grade-separated roads (MassPike, Storrow Dr, Mem Drive overpass), they have been filtered out of the crash analysis.

A Low-Cost, Quick-Build Proposal to Address

All These Problems

1. Bike safety
• Protected bike lanes
• Signal Separation at the Comm. Ave. and Mem Drive intersections
• Safety improvements to the Cambridge-side rotary

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• Pedestrian safety and service
• Longer head-start over conflicting right turn traffic at Comm Ave
• Synchronized pedestrian phases for the crossings along Mem Drive
• Also, protected bike lanes = fewer bikes on the sidewalks
• Get southbound buses out of crippling congestion
• Increase southbound capacity at the Comm. Ave. and Mem Drive intersections (signal timing adjustments)
• Bus lanes in the rotary
• Delivers improved safety & less congestion for autos, too.

Bike Safety (a): Protected bike lanes

Current

No separation from traffic.

Approaching Comm. Ave., a “pocket bike lane” between two car lanes.

Proposed

a. Add flexpost-separated bike lanes for full length of the bridge. Flexposts would be placed along the inside edge of the existing bike lanes without altering the width of the existing travel lanes, just as MassDOT did on the Charles River Dam Bridge and as Brookline did on Harvard Street. The BU Bridge bike lanes are 5 inches wider than those on Harvard Street, so there’s enough space them. Short flexposts (24 inches high) are preferred; they won’t interfere with most bikes’ handlebars.

b. Instead of a pocket bike lane, keep bike lane against the curb. Approaching Comm. Ave., the bike lane and right turn lane will essentially swap positions.

Bike safety (b): Signal Separation between bikes and right-turning traffic at both Comm Ave and Mem Drive.

Distinct phases for bikes leaving the bridge and right turns at both the Comm Ave and Mem Drive intersections

bike

car

Now: Bikes and turning cars get green at the same time

(illustration at the Mem Drive intersection)

15 s

30 s

car

bike

ped

Instead, there should be one phase serving bikes leaving the bridge, and a distinct phase for right turns

NOT radical: At the Comm Ave intersection, signal separation is already in place protecting bikes riding along Comm Ave in both directions. Bikes leaving the bridge need the same protection.

Same thing needed at the Comm Ave intersection

45 s

Bike safety (c): Safety Improvements in the Rotary

• Raised pedestrian and bike crossings at unsignalized crossings buses don’t traverse
• Colored (green) bike lanes
• Protective islands to make flow more predictable and create right-angle crossings
• Only 1 exit lane at Brookline Street (shorter crossing)
• Only 1 circulating lane northbound and southbound
• Bike ramp from rotary (heading south) to the shared-use path along Mem Drive
• STOP sign instead of Yield where Mem Drive eastbound downramp meets the rotary (poor visibility)
• And more ...

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Bike Safety (d): A full-width shared use path on the Mem Drive eastbound on-ramp, from the BU Bridge to BU Boathouse

Easy solution:

• Shift the curb, shrinking the roadway to the width of 1 traffic lane
• That will create enough space for a two-way cycletrack and a sidewalk

There’s a bike lane for bikes going up, but bikes coming down the ramp have to use the narrow sidewalk.

Pedestrian Safety (a): Longer Head Start

First 9 seconds:

Peds, bikes, and thru traffic start first. Pedestrians establish their priority in the crosswalk.

After:

Bikes stop, and turning vehicles begin. Pedestrians continue and complete their crossing. (Bikes get a second green, later in the phase.)

At the Comm. Ave. crossing, cars turn right as pedestrians cross. Currently, to mitigate this conflict, pedestrians get a 4-second head start using the technique called Leading Pedestrian Interval. With signal separation (described earlier), pedestrians will instead get a 9-second head start, using a technique called Leading Thru Interval.

Here’s how signal separation and Leading Thru Interval can work together at the Comm Ave intersection

Pedestrian Safety (b): Synchronize crossings so that pedestrians don’t have to wait twice, & eliminate pushbuttons

Ideally, shift the crossings to the south as pictured above. That will reduce the full crossing distance, making it easier for pedestrians to cross in single pass.

For pedestrians walking along Mem Drive, the signals for the two crossings (at the bridge exit, at the bridge entrance) are currently uncoordinated, and the crossings are pushbutton actuated.

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With signal separation (described earlier), the cycle lengths at the two signals can become the same, allowing the crossings to be coordinated so that most people can make both crossings without stopping in the middle. Pedestrian phases can become automatic, eliminating the need for anyone to push a button.

Note: The bike safety improvements to the rotary on the Cambridge side provide a third round of safety improvements for pedestrians.

Reducing congestion and bus delay (a): Signal separation makes traffic signals more efficient at the Comm Ave. Intersection.

With signal separation and Leading Thru Interval,

• thru traffic no longer has to be held for 4 seconds during LPI if there is a Leading Thru Interval instead
• red clearance time can be reduced by 5 seconds if bikes are controlled separately

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Result: More green time for thru traffic leaving the bridge, increasing capacity by 13%, thus reducing congestion and bus delay.

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Reducing congestion and bus delay (b): Pedestrian Coordination facilitates longer green time for traffic entering the BU Bridge.

The signalized pedestrian crossing at the bridge entrance is the main bottleneck for southbound traffic.

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With coordination and automatic pedestrian phases, there can be more green time for cars and buses, increasing capacity by about 15% and thus eliminating most of the congestion that now cripples bus service.

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Even with more green time for cars, pedestrian delay will be reduced because the pedestrian phases will be coordinated.

Increasing southbound throughput at the signals on both the Cambridge side and the Boston side will make bus delay fall drastically.

Reducing bus delay (c): Bus lanes in the Rotary

bus + bike lane

bus lane

Here, a full car lane has been closed and is currently hatched out. Make it a bus lane!

Here, too, a car lane has been closed, and has been replaced with a bike lane and hatched out buffer. It can instead become a bus-bike lane.

Note: bikes also have the option of using the shared use path.

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Better yet: an exclusive bus lane here, provided the shared use path is appropriately widened so that bikes don’t need a bike lane

Multi-jurisdictional - needs a coordinated solution with a clear champion

• City of Cambridge owns streets approaching the bridge
• DCR owns Memorial Drive, the Cambridge-side rotary, and its intersection with the BU Bridge
• MBTA operates bus service over the bridge
• MassDOT owns the BU Bridge and its intersection with Comm Ave
• City of Boston coordinates and operates traffic signals along Comm. Ave.
• Town of Brookline owns streets on the south side of the Comm Ave intersection

Recap:

A Low-Cost, Quick-Build Proposal that Makes the BU Bridge Better for All

• Bike safety
• Protected bike lanes
• Signal Separation at the Comm. Ave. and Mem Drive intersections
• Safety improvements to the Cambridge-side rotary
• Widened paths along Mem Drive

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• Pedestrian safety and service
• Longer head-start over conflicting right turn traffic at Comm Ave
• Synchronized pedestrian phases for the crossings along Mem Drive
• Also, protected bike lanes = fewer bikes on the sidewalks
• Get southbound buses out of crippling congestion
• Increase southbound capacity at the Comm. Ave. and Mem Drive intersections (signal timing adjustments)
• Bus lanes in the rotary
• Delivers improved safety & less congestion for autos, too.

• Grey Black - Boston Cyclists Union
• Preston Buehrer
• Ken Carlson - Rt 16 Traffic Calming Coalition
• Chris Cassa - Memorial Drive Alliance, Cambridge Bike Safety
• Peter Cheung - Boston Cyclists Union
• Charlie Dennison - Livable Streets Alliance
• Dorothy Fennel - Longwood Collective
• Peter Furth - Northeastern University, Boston Cyclists Union
• Crystal Huff - Mutual Aid Medford and Somerville (“MAMAS”)
• Janie Katz-Cristy - Memorial Drive Alliance
• Scott Kilcoyne - Cambridge Bicycle Advisory Committee

BU Bridge Safety Alliance

• David Kroop - Biking Brookline
• Carl Larson - Boston University
• Steve Miller - Livable Streets Alliance
• Galen Mook - MassBike
• Ari Ofsevit - Memorial Drive Alliance
• Austin Paul
• Rani Schloss
• Nathan Phillips - Boston University
• Dave Read - Longwood Medical Area Cyclists Network
• Jeff Rosenblum - Livable Streets Alliance
• George Schneeloch - Somerville Bike Safety
• Petru Sofio - MassBike
• Randy Stern - Cambridge Bicycle Advisory Committee, Cambridge Bike Safety

Appendix

What’s up with the BU Bridge?

It’s Narrow!

70’: North Washington (when complete, including separate bike lanes)

66’: Craigie Bridge (Museum of Science)

52’: Harvard Bridge (Mass Ave)

52’: Longfellow

40’: BU Bridge

3 narrow lanes + bike lanes, all very narrow, OR four narrow car lanes without bike lanes.

What’s up with the BU Bridge?

It’s Short! Distance between signals:

3500’: Longfellow

2200: Harvard Bridge (Mass Ave)

1700’: North Washington (when complete, including separate bike lanes)

1300’: Craigie Bridge (Museum of Science)

1000’: BU Bridge

Traffic lights are interrelated (but not coordinated), w/minimal “storage” for vehicles on the bridge.