Although accident statistics have an important monitoring function and may form a basis for detecting specific traffic safety problems, the information as available from accident data is inadequate for the next steps in studying safety problems, viz. analysis and diagnosis definition of remedial measures, and evaluation of effects. Systematic observations of road user behaviour, combined with knowledge of human information processing capabilities and limitations, offer wider perspectives in understanding the causes of safety problems. With such an approach it is important to distinguish critical from normal behaviour. A video based observation and analysis method was developed that permits objective that permits objective quantification of dynamic characteristics of road user behaviour in various situations. The results of several studies point to the direct use of time-related measures in road users' decision making in traffic. Examples are Time-To-Collision (TTC) for the severity ranking of traffic conflict and Time-To-Intersection (TTI) for approaching and negotiating intersections. Some examples of recent research are discussed and it can be concluded that road users display fairly consistent behavioural patterns dependent on the type of priority regulation, and that normal and critical behaviour are well distinguished by applying a minimum value of 1.5 seconds as a criterion.
Abstract