Influence of traffic signal timing on red-light running and potential vehicle conflicts at urban intersections

August 1997

Motor vehicle crashes at traffic signals are a major source of injuries and property damage, especially in urban areas. Many crashes result from vehicles entering the intersection after the onset of a red light, a traffic violation that may be affected by the duration of the change interval (the yellow and all-red periods of the traffic signal). The purpose of this study was to examine short-term and sustained effects on red-light compliance and potential vehicle conflicts as a result of an increase in change intervals to values associated with the Institute of Traffic Engineers (ITE) proposed recommended practice for determining vehicle change intervals. Data were collected during an experiment in an urban location involving changes in signal timing at some 10 intersections. Observations included the proportion of signal cycles with vehicles entering on a red light and the proportion of vehicles exiting the intersection after the onset of a conflicting green signal. Results indicate that change intervals set closer to ITE's proposed recommended practice can reduce redlight violations and potential right-angle vehicle conflicts and that such safety benefits can be sustained.