FAQ - Pros and Cons of Traffic Signals

While many people realize that traffic signals can reduce the number of angle collisions at an intersection, few realize that signals can also cause an increase in other types of accidents. For example, it has been well documented that other types of accidents, notably rear-end collisions, usually increase when a signal is installed.

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Normally, traffic engineers are willing to trade off an increase in rear-end collisions for a decrease in the more severe angle accidents; however, when there is no angle accident problem at an intersection, there is nothing to trade off, and the installation of traffic signals can actually cause a deterioration in the overall safety at the intersection. Traffic signals should not be considered a "cure-all" for traffic congestion, and the primary goal of all traffic engineers is to attain the safest and most efficient traffic flow feasible.

In addition to an increase in accident frequency, unjustified traffic signals can also cause excessive delays, disobedience of signals and diversion of traffic to inadequate alternate routes.

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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 $80,000 and $100,000 to install, depending on the complexity of the intersection and the characteristics of the traffic using it. On top of this, there is the perpetual cost of the electrical power consumed in operating a signalized intersection 24 hours a day. This cost now averages about $1,400 per year.

Traffic Control Signal Advantages

Traffic control signals that are properly located, operated and maintained may have one or more of the following advantages:

• Signals may provide for the orderly movement of traffic by assigning right-of-way to conflicting movements of traffic.
• Signals may increase the traffic-handling capacity of an intersection by permitting conflicting streams of traffic to share the same intersection.
• Signals may reduce the frequency of certain types of accidents, especially right-angle (broadside) collisions.
• Signals may provide for continuous movement and progression of traffic through coordination with surrounding traffic signals.
• Signals may interrupt heavy traffic to allow both vehicular and pedestrian traffic to cross.

Traffic Control Signal Disadvantages

Traffic control signals may have one or more of the following disadvantages:

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• Signals may increase delay both overall intersection delay and/or specific movement delay.
• Signals may encourage the use of alternate and/or less adequate routes by drivers wishing to avoid the signal.
• Signals may encourage increased volumes of traffic on the minor street by drivers wishing to use the signal.
• Signals may encourage disobedience and disregard of traffic control devices. (During periods of lesser volume on the main street, drivers on the minor street may have sufficient gaps to cross and/or enter traffic, but be prohibited from doing so by the signal.)
• Signals may cause an increase in the frequency of certain types of accidents, especially rear-end collisions.
• Signal can decrease the vehicle-carrying capacity of the roadways on which they are placed.