Traffic Signals
Traffic signals are an important part of the transportation network. They control the flow of all modes of traffic at our busiest intersections. TP&T engineers are responsible for designing, operating and maintaining all traffic signal equipment on Cambridge roadways.
When carefully and thoughtfully designed, traffic signals can provide a safe and efficient route through intersections for pedestrians, bicycles, and vehicles. On this page we will discuss the features of Cambridge traffic signals. Also you can read the Department’s written Traffic Signal Policy. For more about traffic signals as they relate to walking, please click here.
Aside from the traditional red-yellow-green traffic signals, which engineers call “stop-and-go” signals, we also own and operate school zone flashers and warning beacons.
Stop-and-Go Traffic Signals
The TP&T owns and operates 133 stop-and-go traffic signals. Additionally there are 34 signals that are within the Cambridge city border but are owned and operated by the District of Conservation and Recreation or MassDOT, both state agencies.
Our traffic signals have many features that help protect the safety of pedestrians and bicyclists, which are more vulnerable road users. These include Leading Pedestrian Intervals, Countdown Pedestrian Signals, Audible Pedestrian Signals and Protected Turns.
Leading Pedestrian Intervals
At many Cambridge traffic signals, pedestrians are permitted to cross the street at the same time as the green light. At those locations, the WALK sign comes on 3 to 5 seconds before the green light, which gives pedestrians a chance to start walking and occupy the crosswalk space before the first car has a chance to make a turn.
For more detail on concurrent pedestrian phasing please click here.
Countdown Pedestrian Signals
At most Cambridge intersections with traffic signals, we have upgraded the pedestrian signals to signals that include a countdown legend. The legend indicates how much time, in seconds, pedestrians have remaining to cross the street.
Countdown signals provide pedestrians with more information than the traditional WALK and DON’T WALK indications. In Cambridge, flashing DON’T WALK intervals are based on a walking speed of 3½ feet per second, but many people walk faster than that pace and some slower. With the countdown signal, there is no mystery to how much time is left and each person can decide if there is enough time to cross.
Audible Pedestrian Signals
In partnership with the Cambridge Disabilities Commission, TP&T has begun to install modern, pole-mounted audible pedestrian signals (APS). The new units will replace older units that are mounted to the pedestrian signals and made tapping, drumming, or chirping tones. The devices are intended to aid the visually impaired.
Each unit is fully programmable with a laptop computer via a USB cable. Any of several dozen settings can be adjusted, including volume levels and the nature of the audible tones. The units are programmed so that the WALK sign audible message will activate only when the button is pressed. Only the locator tone, which is designed to be heard within only 10 feet of the pole, will be active at all hours.
Protected Turns
Turns at traffic signals fall into one of three categories: Permitted, Protected, and Permitted-Protected. At smaller intersections, turns are usually permitted, meaning the motorists may turn left or right after yielding to other vehicles and all pedestrians and bicyclists. With a protected turn, the motorist is shown a green arrow and may turn only when the arrow is shown. (Permitted-Protected is when a combination of the above is used.) At our larger intersections, we have been converting permitted turns – especially left turns – to Protected only. When a turn is protected, pedestrians, bicyclists, and other vehicles are protected as well because they are programmed to use the intersection during a different time in the signal cycle.
The City is testing out the HAWK, a new type of traffic signal at Sixth & Binney Streets. HAWK, which stands for High intensity Activated crossWalK, contains two adjacent red lights and one yellow light. Pedestrians activate it upon arrival. The new light protects pedestrians like a regular traffic signal, yet allows vehicles to proceed through intersection when the crosswalk is empty.
Indicators:
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When no lights are on, it is safe to drive through, but watch for pedestrians.
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Flashing yellow means button has been pushed, so watch for pedestrians.
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When yellow light stops flashing, drivers should stop if able to do so safely.
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When two red lights come on. STOP. The WALK sign is on and pedestrians are crossing
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When red lights start flashing, if crosswalk is empty, drivers can proceed after stopping, as if there is a stop sign.
View Diagram of Indicator light states.
School Zone Flashers
These devices are programmed to activate during school pick-up and drop-off times. When activated the speed limit on the street is 20 MPH. TP&T maintains 34 school zone flashers.
Warning Beacons
Single flashing yellow or red signals are used at some intersections. Nineteen intersections use these devices.
For more information on the content of this page, please contact us here.