ESTIMATING THE SAFETY OF UNSIGNALIZED INTERSECTIONS USING TRAFFIC CONFLICTS

The deficiencies of motor vehicle accident records have long been recognized as an obstacle to a complete understanding of traffic safety problems at intersections. The Traffic Conflict Technique was developed to provide additional information that could help make up for the deficiencies of accident records. This paper describes the application of the traffic conflict technique to the estimation of safety at unsignalized intersections. A computer simulation model, TSC-Sim, is used to study traffic conflicts with time-to-collision as the critical traffic event in simulating driver behavior. Some aspects of the gap-acceptance criteria, in addition to the differential effects of several driver characteristics (e.g., age, sex, and waiting time tolerance), are examined. The effects of traffic flow characteristics, such as speed and volume, on the number and severity of conflicts are also discussed. Using the data collected from 30 conflict surveys, traffic conflict frequency and severity standards for unsignalized intersections have been established. These standards allow the relative comparison of the conflict risk at various intersections. An Intersection Conflict Index measure was established to summarize the intersection conflict characteristics.