1. Peter G Furth Zhao Sha Sara Rauwolf Northeastern University
Bike Lanes and Informal Flares:
Making Longwood Avenue Safe and
Functional for All Users
Peter G Furth
Zhao Sha
Sara Rauwolf
Northeastern University

2. On Longwood Ave, Are Bicyclists Intended* and Valued Users?
Historical answer?
“No.”
Modern answer?
“Of course!”
Road layout’s answer?
“I’m historical.”
* As opposed to merely tolerated

3. Longwood Ave’s 32 Foot Constraint
Car-Bus lanes: 10 to 11 ft
Bike lanes: to 6 ft
So if cars “need” 2 thru lanes plus a left turn lane …
At Brookline Ave eastbound each cycle:
2 cars turn left
10 bikes
So why a left turn lane, but no bike lane???

4. Left Turn Lanes: Not for the Left-Turning Cars, but for the Other Cars!

5. Informal Flares: Preventing Blockage without a Left-Turn Lane
Longwood St Paul Street, Brookline

6. Bike Lanes Can Help Create an Informal Flare
St Alphonsus Tremont St, Boston

7. 18 Ft Makes an Informal Flare
With a 32 ft constraint:
4’ ’ ’ ’

8. Traffic Simulation Demonstrates Feasibility
Weekday, A.M. Peak Hour Volumes
No change to boundary traffic signals (Riverway, Huntington Ave.)
Uses VISSIM microsimulation software
See the simulation

9. Is It Safe for Bikes? Cars enter bike lanes routinely
Right turns
Parking
Getting around left-turning cars
Line makes lane-changing right of way unambiguous and therefore safer

10. What the Highway Capacity Manual Says about Informal Flares
[nothing]
Options using Synchro* to account for informal flares:
Model it as a short, narrow left turn lane
There will be ample capacity if there are only a few left-turning cars per cycle)
Ignore it
Blockage caused by left-turning cars results in a capacity disaster
* Best known software for intersection capacity, based on Highway Capacity Manual’s macroscopic formulas

11. With bike lanes sized to serve as informal flares, it’s possible.
Making Longwood Avenue Safe and Functional for All Intended Users
With bike lanes sized to serve as informal flares, it’s possible.

12. Why Mixed Traffic Doesn’t Work
Green light: Cars need to pass bikes
Cars & bikes single file would be a capacity disaster
Red Light: Bikes need to pass cars
Bikes need to be advance to the head of the queue in order to be visible & safe