The first electric signal in the United States was installed in Cleveland, Ohio in 1914. From these modest beginnings, traffic signal technology has greatly expanded and has become a critical element in the safe and efficient control of traffic on our streets and highways. Traffic signals are used to assign vehicular or pedestrian right of way. By providing alternate right of way traffic signals exert a profound influence on traffic flow and can operate to the advantage or disadvantage of the vehicles or pedestrians they control.
A careful analysis of traffic operations and other factors at a large number of signalized and unsignalized intersections, coupled with the judgment of experienced engineers, have provided a series of warrants that define the minimum conditions under which signal installations may be justified.
Traffic signals can not be installed unless one of the warrants specified by the Manual on Uniform Traffic Control Devices (MUTCD) has been satisfied. The MUTCD is a document that is published by the Federal Highway Administration and has been adopted by the Texas Department of Transportation. These warrants are based on a number of factors including: the number of vehicles, pedestrian activity, vehicular speeds, accident history, population of the city, and number of traffic lanes. The satisfaction of a warrant or warrants is not in itself justification for a signal. A traffic engineering study must be conducted to determine if the traffic signal should be installed.
Traffic signals are valuable devices for the control of vehicle and pedestrian traffic. Warranted traffic signals properly located and operated, usually have one or more of the following advantages:
They can provide for the orderly movement of traffic.
Where proper physical layouts and control measures are used, they can increase the traffic-handling capacity of the intersection.
They can reduce the frequency of certain types of accidents, especially right-angle type.
Under favorable conditions, they can be coordinated to provide for continuous or nearly continuous movement of traffic at a definite speed along a given route.
They can be used to interrupt heavy traffic to permit other traffic, vehicular or pedestrian, to cross.
It is unfortunate that traffic signals have become regarded by the public as a panacea or "cure-all" for any and all traffic problems at intersections. The following factors can result from an improper or unwarranted signal installation:
Excessive delay may be caused. Even the best designed and operated signals usually increase delay when compared to unsignalized intersections. However, unnecessary delay is a common feature of an unwarranted or an improperly designed traffic signal. This unnecessary delay results in significant fuel waste and higher motorist costs.
Disobedience of the signal indications is encouraged. Delay at unwarranted or poorly designed traffic signals can breed gross disrespect toward signals a well as other traffic control devices.
The use of less adequate routes may be encouraged in an attempt to avoid such signals.
Accident frequency can be significantly increased at unwarranted signals or at locations where installation was not based on sound engineering analysis. Accidents related to signal control usually develop during periods of comparatively low volume and result from rear-end collisions, and drivers either willfully of unintentionally running the red light.
Traffic signals are much more costly than is commonly realized, even though they represent a sound public investment when justified. A modern signal can cost taxpayers between $150,000 and $250,000 to install depending on the complexity of the intersection and the characteristics of the traffic using it.
On top of this, there is a perpetual cost which is almost never considered - the cost of the electrical power consumed in operating a signalized intersection 24 hours a day, and the associated maintenance costs. These costs can be $1,000 to $2,000 a year.