In light of the recent decision to reinstall a traffic light at the intersection of Elm and Margaret streets, I felt compelled to clarify serious misconceptions that persist about traffic signals.
The basic question that must be answered is: Will this intersection operate better with or without a traffic signal?
First and foremost, traffic signals are used to assign vehicular and pedestrian rights-of-way. They are used to promote the orderly movement of vehicular and pedestrian traffic and to prevent excessive delay to traffic.
The idea that an intersection is any safer due to a traffic signal is not necessarily true, as is shown in a multitude of studies and data. In fact, unjustified or improper traffic-control signals can result in one or more of the following disadvantages: excessive delay, excessive disobedience of the signal indications, increased use of less adequate routes as road users attempt to avoid the traffic-control signals and significant increases in the frequency of crashes (especially rear-end crashes).
Secondly, a traffic signal does not resolve all traffic problems at an intersection. Traffic-control signals are often considered a panacea for all traffic problems at intersections. This belief has led to the installation of signals at many locations where they are not needed and where they may adversely affect the safety and efficiency of vehicular, bicycle and pedestrian traffic.
Lastly, traffic signals should not be installed unless one of the warrants specified by the Manual on Uniform Traffic Control Devices has been satisfied. An engineering study must be conducted to determine whether the traffic signal should be installed.
The installation of a traffic signal requires sound engineering judgment and must balance these sometimes conflicting goals: moving traffic in an orderly fashion, minimizing delay to vehicles and pedestrians, reducing crash-producing conflicts and maximizing capacity for each intersection approach.