Safety Impacts of Photo-Red Enforcement at Suburban Signalized Intersections

Abstract

Photo-red enforcement entails cameras that photograph a vehicle entering an intersection after the traffic signal has turned red; a citation is then mailed to the vehicle's owner. Such a program was operated at 13 signals in Fairfax County, Virginia, between 2000 and 2005. This paper reports how photo-red enforcement affected crash frequency at the intersections. An empirical Bayes approach was used to detect the impact of the program on crashes while main-line traffic volume, yellow time, truck percentage, number of left-turning lanes, and speed limit were controlled. Cameras were definitely correlated with decreased red light running crashes (11% to 55%), increased rear-end crashes (32% to 85%), increased total crashes (0% to 23%), and decreased red light running injury crashes (5% to 64%). Cameras were probably associated with increased total injury crashes (5% drop to a 33% raise). These results are consistent with those of other studies with one notable exception: In the case of Fairfax County, the magnitude of the increase in rear-end crashes was larger than the magnitude of the decrease in angle crashes. That difference from other studies may have been the result of the investigators’ decision to study the crash narrative and diagram instead of relying only on collision type. Because the number of induced rear-end crashes was so much larger than the number of eliminated red light running (angle) crashes, a net safety gain would be realized if and only if severity of the latter were substantially greater than severity of the former.