Traffic signals are used to control the right of way at intersections. Strict engineering guidelines are published in the Manual on Uniform Traffic Control Devices (MUTCD) that engineers use to determine if a traffic signal is "warranted". The warrants provide consistent national balance between mobility, safety, efficiency, and costs. However, signalized intersections are often viewed by the general public as safer than unsignalized intersections. This belief is often heightened when there are personal injuries and even higher when children are involved. Parents, city officials, and local interest groups often vigorously request the installation of a traffic signal. After these requests are received, an engineering study is performed, and a traffic signal is often determined to be not warranted. It is the traffic engineer's responsibility to explain to the public why a signal is not needed. These results are not the desired response and in turn the public becomes more diligent for their cause and the cycle continues. This cycle of request and denial for a traffic signal is often seen at intersections adjacent to schools. This report examines signal installations at minimally warranted intersections between 1991 and 1999. Before and after accident data were analyzed at each of these intersections showing a difference in annualized crash rates for accident type and severity. The data suggest that for intersections not meeting warrants defined by the MUTCD, traffic signals should not be installed.
Abstract