Traffic Signals

Learn How the Signals Operate

Each year the City receives inquiries concerning the operation of traffic signals. The public’s understanding of the function of traffic signals can improve driving habits by reducing speeding and associated traffic accidents. The more drivers know about the operation of traffic signals the less they will be frustrated when waiting for a signal to change.

Why are traffic signals needed?

As traffic volumes increase beyond the capability of lesser controls such as a four-way stop, it may be necessary to install a traffic signal. Before installing a traffic signal at an intersection, established minimum criteria must be satisfied. A review includes:

  • Are traffic signals the answer to solving traffic problems?
  • Special conditions such as hills and curves;
  • The accident history of the intersection; and
  • The amount of vehicular and pedestrian traffic;
  • The need to provide interruption to the major flow for side street vehicles and pedestrians;
  • The proximity of schools

Advantages of Traffic Signals

Signals offer maximum control at intersections. They relay messages of both what to do and what not to do. The primary function of any traffic signal is to assign right-of-way to conflicting movements of traffic at an intersection. This is done by permitting conflicting streams of traffic to share the same intersection by means of time separation. By alternately assigning right-of-way to various traffic movements, signals provide for orderly movement. They may interrupt extremely heavy flows to permit other traffic to move safely through an intersection.

When properly timed, a traffic signal increases the traffic handling capacity of an intersection. When installed under conditions that justify its use, a signal is a valuable device for improving the safety and efficiency of both pedestrian and vehicular traffic. In particular, signals may reduce certain types of accidents, most notably right-angle (broadside) collisions.

Disadvantages of Traffic Signals

While many people realize that traffic signals can reduce the number of broadside collisions at an intersection, few realize that signals can also cause a significant increase in rear-end collisions. Normally, traffic engineers are willing to accept an increase in rear-end collisions for a decrease in the more severe broadside accidents. However, when there is no broadside accident problem at an intersection and a signal is not needed for traffic control, there is minimal safety benefit and the installation of traffic signals can actually decrease overall safety.

Traffic signals are not a “cure-all” for traffic problems. The primary goal of the traffic engineer is to attain the safest and most efficient overall traffic flow possible. In addition to an increase in accident frequency, unjustified traffic signals can also cause excessive delay, promote disobedience of signals, and divert traffic to residential streets.

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