Transportation Infrastructure

Benefits of Traffic Control Signal Systems Are Not Being Fully Realized Gao ID: RCED-94-105 March 30, 1994

Traffic congestion, particularly in cities, pollutes the air, jeopardizes safety, impedes energy conservation, and results in aggravating delays. Its adverse effects on the local and national economy are pegged at $40 billion annually. Although adding more road capacity can reduce traffic congestion, states and localities can also reduce congestion through transportation control measures, such as improving public transit, encouraging employers to provide incentives for carpooling, and making better use of existing roads with effective traffic control signal systems. This report discusses (1) the benefits of traffic control signal systems; (2) the problems that state and local agencies face in implementing, operating, and maintaining effective signal systems; (3) the relationship of the current signal systems to emerging technologies like Intelligent Vehicle/Highway Systems; and (4) the role of the Federal Highway Administration in assisting state and local governments with their signal systems through reviews of plans and other measures. GAO also provides related information on the operation of traffic control signal systems, such as left and right turns on red signals and the practice of running red signals.

GAO found that: (1) state, local, and transportation industry studies have shown that upgrading traffic control signals and changing traffic signal timing can reduce local accidents, congestion, travel time, fuel consumption, and air pollutants; (2) states and localities have experienced problems with traffic signal effectiveness because they have not properly designed, operated, and maintained their signal systems; (3) of the 24 systems FHwA reviewed, 21 did not meet minimum performance standards and some localities were designing outdated systems; (4) in 1989, 74 percent of urban signalized intersections needed upgraded physical equipment or improved signal timing; (5) state and local governments often lack sufficient resources to operate and maintain their signal systems; (6) older signal systems do not provide sufficient traffic volume and flow data needed to support emerging traffic signal technology development; (7) the benefits from emerging technologies may not be realized if states or localities continue to experience operating and maintenance problems and resource constraints; (8) FHwA does not consistently review state and local governments' traffic signal operating plans and it does not have sufficient technical expertise to assist state and local governments with their traffic control signal systems; and (9) FHwA needs to clarify the role of its field offices, issue guidance on preparing operations plans, and develop the necessary expertise to assess the current and future benefits of existing and emerging traffic control signal systems.


Our recommendations from this work are listed below with a Contact for more information. Status will change from "In process" to "Open," "Closed - implemented," or "Closed - not implemented" based on our follow up work.

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