Driver Behavior, Dilemma Zone, and Capacity at Red Light Camera Equipped Intersections

Driver behavior at an intersection equipped with a Red Light Camera (RLC) is one of the main factors contributing to the safety and operation of the intersection. A drivers’ decision whether to proceed through the intersection or stop when the signal changes from green to yellow depends on a number of factors, such as speed, geometric characteristics, driver’s attitude, to name a few. The decision with respect to the yellow signal may lead to traffic conflicts such as rear end and right angle collisions. Driver behavior when faced with a yellow signal can be viewed as a binary choice process, where the main decisions are either to stop or proceed through the intersection. In this paper, a discrete choice model of the stopping probability is developed using vehicles’ speed and distance from the stop bar when the driver is exposed to the yellow signal. A binary choice model is developed using the probability of stopping to the yellow signal as a function of approach speed, distance from intersection, and presence of a RLC. The existence of the Dilemma Zone (DZ) is estimated using dilemma zone curves developed from the probability of stopping vs. distance from stop bar at the onset of the yellow interval. The paper also presents a new approach to calculate the change in intersection capacity resulting from drivers stopping at the intersection at the onset of yellow interval. Using field data from Baltimore, Maryland we show that the capacity of RLC equipped intersections may be lower than that at intersections without RLC.