Modelling risk is one of the elements needed for modelling driver behaviour to understand driver behaviour and to develop criteria for testing and evaluating in-car information and driver-support systems that interact with the driver. The results of several studies point to the direct use of time-related measures such as Time-To-Collision (TTC) and Time -to-Line-Crossing (TLC) as a cue for decision-making in longitudinal and lateral control of the vehicle. This paper deals with the issue of distinguishing normal from critical interactions between road users based on the minimum TTC measure as derived from several traffic conflict observation studies and additional experimental research. The latter reveals that both the decision to start braking and the control of braking may well be based on TTC information directly available from the optic flow field. Studies on driver behaviour in fog enable a precise definition of critical situations relevant for a proper criterion setting for Collision-Avoidance Systems (CAS). A similar approach for a time-based description of driver behaviour when negotiating intersections in terms of Time -To-Intersection (TTI) and Time-To-Stopline (TTS) together with the TTC measure provides suitable input for modelling driver behaviour as a basis for Intersection Collision Avoidance Warning Systems. (Author/publisher)
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