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Back Bay Traffic Signal Retiming Project Underway

October 29, 2014


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Traffic signals at 62 locations in Boston’s Back Bay are in the process of being retimed as part of a Boston Transportation Department program designed to ensure that equipment settings at the city’s 841 signalized intersections meet the existing demand from all users of local streets.  The Back Bay phase of the program began in September and is expected to be completed by next spring.

Boston Mayor Martin J. Walsh said, “Taking proactive steps to upgrade traffic signal timing so that it meets the current travel needs of pedestrians, cyclists and drivers, is a smart and resourceful operational plan.  Updating the coordination of our traffic signals will improve safety, reduce congestion and help us to meet our environmental goals.”

“The objective of signal timing is to respond to the demands of motor vehicles, pedestrians and bicycles in an optimal manner,” said Interim Boston Transportation Department Commissioner James E. Gillooly.  “This includes establishing a balanced scheduled that provides a sufficient amount of time for all users to travel through intersections and on streets safely and efficiently.”

As part of the process, an assessment is made to collect data on the following existing factors:

  • Lane Configurations
  • Geometrics
  • Vehicle, Bicycle and Pedestrian Counts
  • Pedestrian Crossing Distances
  • Existing Signal Operation
  • Accident Data
  • Traffic Queue Lengths
  • Travel Times.

In addition to field observations, the data is entered into Synchro, a traffic simulation and optimization software, where a model of the intersection and/or roadway is created that is then calibrated to match existing conditions.  Traffic engineers enhance the traffic signal timing by adjusting signal cycle lengths, the amount of green time given to motorists and bicyclists traveling on each street, vehicle clearances and the amount of time required for pedestrians to cross.  The federal government has recently mandated the use of a slower walking speed from 4 feet per second to 3.5 feet per second to calculate pedestrian crossing time.  This will result in a slightly longer crossing time depending on the length of the crosswalk.

Adjustments will also be made to update the synchronization using new traffic data.  The goal is to improve the progression along city streets while minimizing the number of stops and delays for all users.

On average, signal timing updates typically reap the following benefits:

  • Reduce Driver Delays by 23.6%
  • Reduce Travel Times by up to 25.0%
  • Reduce Vehicular Emissions by 12.0%
  • Reduce Fuel Consumption by 12.2%
  • Reduce Vehicle Crashes by 8%.

The new traffic signal timings for the Back Bay will be entered into a database at BTD’s Traffic Management Center.  The Traffic Management Center provides engineers with the ability to control traffic signals remotely from City Hall.  The effect of the new timings will be monitored via both field observations and video feed from traffic cameras, and BTD will fine-tune the new signal timings as appropriate.