The use of adequate yellow signal timing reduces red light violations and injury related crashes, but longer yellow timing used in conjunction with red light cameras provides a more significant decrease in incidents of red light violating. The Insurance Institute for Highway Safety recently conducted a field study to evaluate the effects on red light running by first lengthening yellow signal timing, followed by the introduction of red light cameras. Six approaches to two different intersections were tested sequentially. Findings were compared against three intersections in a neighboring city where red light cameras were not used and yellow light timing remained constant. Results showed that yellow timing changes reduced red light violations by an average 36 percent. The addition of red light camera enforcement further reduced red light violations by 96 percent beyond levels achieved by the longer yellow timing. At the intersection with the greatest incidence of red light violations—251 per 10,000 vehicles—yellow light extensions reduced the violations to 198 incidents per 10,000 vehicles. Once red light cameras were installed at that intersection, incidents of red light violating dropped to an astounding two per 10,000 vehicles.
Source: Insurance Institute of Highway Safety, Status Report, Vol. 42, No. 1 January 27, 2007; Retting, Richard A., Ferguson, Susan A., Farmer, Charles M., Reducing Red Light Running Through Longer yellow Signal timing and Red Light Camera Enforcement: Results of a Field Investigation, Insurance
Institute for Highway Safety, January 2007.