Standards for traffic control signals are important because traffic control signals need to attract the attention of a variety of road users, including those who are older, those with impaired vision, as well as those who are fatigued or distracted, or who are not expecting to encounter a signal at a particular location.

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:

• They provide for the orderly movement of traffic.
• They increase the traffic-handling capacity of the intersection.
• They reduce the frequency and severity of certain types of crashes, especially right-angle collisions.
• They are coordinated to provide for continuous or nearly continuous movement of traffic at a definite speed along a given route under favorable conditions.
• They are used to interrupt heavy traffic at intervals to permit other traffic, vehicular or pedestrian, to cross.

Information obtained from MUTCD / FHWA Website