Our traffic signal inventory includes flashing 20 MPH school zone signs, intersection warning beacons, and stop-and-go (red/yellow/green) signals.  The purpose of these devices is to provide for the safety of private vehicles, transit vehicles, bicycles, and pedestrians.  The Department designs its traffic signals to provide the following:

*   Allocation of the right-of-way in the safest way possible among all modes of transportation
*   Maximum comfort and convenience for people crossing intersections on foot
*   Reduction of red light running and its consequences
*   Efficient movement of vehicles along arterial corridors for vehicles that are traveling at
     below the speed limit

The Department owns and operates a total of 205 traffic signals, including:
*    136 stop-and-go signals
*    35 intersection warning beacons
*    34 school zone flashers

An additional 35 traffic signals are within the City boundary, but are operated by the District of Conservation and Recreation.

Some specific features of our traffic signals include:

*  Light-Emitting Diode (LED) Lamps:  Not only LED lamps brighter than the old 
    incandescent lamps, they also last much longer and consume far less energy.
*  Countdown Pedestrian Signals:  In addition to the traditional WALK and DON'T 
    WALK symbols, countdown signals display the number of seconds remaining until the end
    of the pedestrian phase.  These signals help make it easier for the pedestrian to decide
    whether to start crossing.   A total of 84 of these signal heads are in use at 21 intersections.
*  Leading Pedestrian Intervals (LPI):  This is simply a head start for pedestrians at 
    intersections where cars and pedestrians are allowed to cross an intersection at the same
    time.  At intersections with LPI, the WALK sign is turned on 3-5 seconds before the
    green light, so that the first vehicle intending to turn right or left is forced to yield to the
    group of pedestrians that has already started to cross.  So far, more than half of the
    intersections eligible have been equipped with LPI.
*  Audible Pedestrian Signals:  Many intersections are equipped with units that
    produce and audible tone (a chirp or a tap) when the WALK sign is on.  The device
    is intended to assist the visually impaired.
*  Traffic Operations Center: Over 50 intersections are connected to the traffic
    operations center where they are monitored 24/7.  Traffic signal programming can be
    downloaded from and changes to the programs can be uploaded to these signals remotely.

Please contact the Traffic Engineering office at (617) 349-4715 with any questions about the City of Cambridge traffic signal system.