Effect of Red-Light Cameras on Capacity of Signalized Intersections

Abstract

Red light running (RLR) is one of the most common violations drivers commit at signalized intersections. To avoid RLR violations, some drivers may decide to stop abruptly, even though they had the opportunity to cross the stop line before the onset of the red light. This action happens more frequently at intersections with a red-light camera (RLC). The consequence of this change in drivers’ stopping behavior is the potential reduction of the usable clearance interval and the slight decline in the intersection capacity. However, different agencies’ guidelines take different approaches to estimate the clearance lost time (CLT) for capacity analysis of signalized intersections; there is not an adjustment factor for considering the impact of RLCs. In an attempt to quantify the effect of RLCs on the capacity of signalized intersections, field data were collected at eight intersections: four with RLCs and four without, in the cities of Opelika and Auburn, Alabama. A total of 1,191 cycles and a total of 1,863 drivers’ responses to clearance intervals were used to estimate the CLT. It was found that the estimated CLT at the approach with a RLC is approximately 2.7 s longer than the default value presented by one set of guidelines and about 1.1 s longer than those in another. On average, the unused yellow time was a half-second longer in RLC intersections than the intersections without RLCs.