TRAFFIC CONFLICTS FOR ROAD USER SAFETY STUDIES

In this paper we advocate an approach to road safety studies in which traffic conflicts are used as indicators of roadway hazard. The critical traffic process event used to define conflict severity is the time to collision, modified by an observer's evaluation of the risk of collision. Field studies were done to assess the validity, reliability, and practicality of traffic conflicts. Experiments were conducted to test the threshold value of time to collision, and to examine a visual perception theory of crash avoidance behaviour. The experiments demonstrate that a time to collision threshold value of 1.5 s is a reasonable time-based index of hazard and that a visual perception model of breaking is a promising concept. The wider potential for traffic conflicts as a measure of driver risk, and as a basis for safety models, is discussed in the paper. The technique has been used for some 45 intersection safety studies. From the application to date it appears that the systematic observation of crash avoidance behaviour of drivers in unsafe conditions provides a useful tool for traffic engineering analysis of intersection traffic control and design problems.