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Traffic Control Signal FAQ

Why do I have to wait so long for a signal to change?
At actuated traffic signals, the green phase for the side street is "triggered" with the detection of a vehicle or the push of a pedestrian push button. Actuated signals are defined as intersections with pushbuttons for pedestrians and detectors for vehicles. The length of delay before the light changes to green depends on when the "call" for a green on the side street was received and if the main street traffic demand has been satisfied. In a coordinated system, the "call" may be held up a short time to maintain main street "progression." In this case, the side street movement can only be serviced after the main street traffic stream has passed through the intersection. The wait time on the side street can vary from a few seconds to upwards of two minutes.

Why do green times on the side streets sometimes seem so short?
Many traffic signals operate in a semi-actuated mode where green times are assigned to the side street based on the traffic volume from that street. When vehicles waiting on the side street clear the intersection before the maximum green time is reached, the green signal will automatically change to amber. By operating in this manner more green time for the main street is provided and the overall operation is made more efficient.

Why does the pedestrian "Don't Walk" signal stay on when the vehicle signal is green?
In order for the pedestrian "Walk" signal to be displayed, the pushbutton must be activated. This guarantees enough crossing time. Crossing against a "Don't Walk" signal is a violation.

Why does the "Don't Walk" signal begin to flash when I am part way across the intersection?
When the "Don't walk" signal begins to flash, it is an indication to pedestrians not to start their crossing as there will not be enough time. Pedestrians should start crossing an intersection only at the beginning of a "Walk" signal.

How much does traffic signal equipment cost?
Traffic Signals are more costly than most people realize. A new signal costs between $60,000 and $150,000 per intersection. The equipment is highly specialized and expensive to maintain and operate, therefore, the decision to install signals must be carefully considered.

How are pedestrian crossing times calculated?
The time for pedestrian "Walk" and "Don't Walk" intervals is based on the distance across the intersection and typical pedestrian walking speeds. At locations where there are a lot of seniors or children, a lower walking speed is used to lengthen the pedestrian "Walk" intervals.

Will a traffic signal be installed at an intersection immediately after a collision or fatality?
Traffic signals don't always prevent collisions and don't always aid traffic control. At some locations, collisions actually increase when signals are installed. Where traffic signals are installed without justification, the potential for pedestrian-vehicle conflict may increase, as motorists do not always recognize the rights of the pedestrian at a crosswalk. When this happens, traffic signals become a liability to safety, rather than an asset.

Why don't all traffic signals have left-turn arrows or flashing greens?
Since there are proper applications for left-turn phases, they should not be overused or implemented at signals that can function effectively and safely without protected left turns. The requirements for left turn phasing are based on the following criteria: the number of left-turns, delay, queue lengths, the number of collisions or conflicts, intersection geometry and signal timing. The implementation of left-turn phasing reduces the amount of green time available for all other movements, and in some cases, left-turn phasing results in the overall interruption of progressive traffic flow.


For more information on any traffic related issues, please contact the following:
 
Traffic & Transportation Engineer
Contact: Enrique Figueredo Kamm, P.Eng

Cornwall