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Advantages and Disadvantages of Traffic Signals

Often the District is contacted by citizens that believe that traffic signal have many advantages and no disadvantages.  While traffic signals can help in locations where they are justified and installed properly, they also have disadvantages.  There will always be some disadvantages even if the signal is justified.  For example, there will be increased delay to major traffic movements as vehicles that do not have to stop without the signal will be required to stop.  Also, while traffic signals can help reduce angle accidents, other types of accidents, especially the rear-end type usually increase with a traffic signal.  It is the job of the traffic engineer to determine when the advantages will outweigh the disadvantages.

Information from the Ohio Manual of Uniform Traffic Control Devices

The entire Ohio Manual of Uniform Traffic Control Devices is available online.  The section relevant to the subject of the advantages and disadvantages of traffic signals is below on this page. 

Section 4B.03 Advantages and Disadvantages of Traffic Control Signals


The following is from section 4B.03 of the Ohio Manual of Uniform Traffic Control Devices:

When properly used, traffic control signals are valuable devices for the control of vehicular and pedestrian traffic. They assign the right-of-way to the various traffic movements and thereby profoundly influence traffic flow. 

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

A.  They provide for the orderly movement of traffic. 

B.   They increase the traffic-handling capacity of the intersection if:

  1. Proper physical layouts and control measures are used, and
  2. The signal operational parameters are reviewed and updated (in needed) on a regular basis (as engineering judgment determines that significant traffic flow and/or land use changes have occurred) to maximize the ability of the traffic control signal to satisfy current traffic demands. 

C.   They reduce the frequency and severity of certain types of crashes, especially right-angle collisions. 

D.  They are coordinated to provide for continuous or nearly continuous movement of traffic at a definite speed along a given route under favorable conditions. 

E.   They are used to interrupt heavy traffic at intervals to permit other traffic, vehicular or pedestrian, to cross. 

Traffic control signals are often considered a panacea for all traffic problems at intersections.  This belief has led to traffic control signals being installed at many locations where they are not needed, adversely affecting the safety and efficiency of vehicular, bicycle, and pedestrian traffic. 

Traffic control signals, even when justified by traffic and roadway conditions, can be ill-designed, ineffectively placed, improperly operated, or poorly maintained.  Improper or unjustified traffic control signals can result in one or more of the following disadvantages:

A.            Excessive delay; 

B.            Excessive disobedience of the signal indications; 

C.            Increased use of less adequate routes as road users attempt to avoid the traffic control signals; and 

D.            Significant increases in the frequency of collisions (especially rear-end collisions). 

Additional information on traffic signals

Determining Need for Traffic Signal Control - Information from the Ohio Manual of Uniform Traffic Control Devices

Engineering Countermeasures to Reduce Red Light Running - From the Federal Highway Administration (FHWA) Internet site.

Intersection Safety: Myth Versus RealityMyths 1 and 4 discuss traffic signals.


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