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Traffic signals are the red, yellow and green lights used at busy intersections to alternately direct approaching traffic to stop and, then, to proceed. When installed at the proper location and under the appropriate conditions, a traffic signal can reduce traffic delays and enhance safety.
There is a widely-held belief that a traffic signal can solve all or most intersection traffic problems. But, under the wrong circumstances, a traffic signal can cause unnecessary delay, waste taxpayer dollars, and actually increase crashes. Simpler measures often work better.
This pamphlet was prepared to provide you with a better understanding about what a traffic signal can do, what it cannot do, what traffic engineers can do to improve safety and reduce delays at an intersection, and what happens when it is determined that a traffic signal is the best solution.
A traffic signal sequentially assigns the right-of-way to vehicles approaching an intersection from various directions, forcing the streams of traffic to take turns entering the intersection. A signal stops traffic in one or more directions so that:
Most signals include vehicle detecting devices, usually imbedded in the roadway, that sense traffic approaching from each direction and adjust signal timing for maximum efficiency.
A signal can reduce the delay to those waiting to enter or cross a heavy stream of traffic and reduce the potentially hazardous conflicts between traffic movements, thereby reducing the likelihood of certain types of collisions. At certain locations it can help establish a "signal progression," where traffic can continue along a route at a reasonable, constant speed and with minimal delay.
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