Behavioural adaptation has been a focal concept in traffic psychology since the mid 1970's. Much effort has been used to define it, and many models have been devised to describe and explain it. However, these attempts sometimes are at risk of confusing the general phenomenon and mechanisms underlying it. This paper defines the behavioural adaptation as a tendency of the driver to react to changes in the traffic system, whether they be in the vehicle, in the road environment, in road and weather conditions, or in his/her own skills or states, and that this reaction occurs in accordance with his/her motives. Very obviously, this kind of adaptive behaviour occurs at many levels of the functional hierarchy of driver behaviour. Therefore, risk-related behaviour should be considered at several levels with different mechanisms to produce behavioural adaptation, often called 'risk compensation'. At a high level, trip decisions modify populations at risk in different circumstances, sometimes attenuating, sometimes amplifying population risk differences. For example, elderly drivers tend to avoid difficult conditions and succeed in keeping the fatality risk per person at a moderate level, while young male drivers at the other end of the continuum use cars very dangerously at nights on weekends. At a low level of vehicle control and guidance in real dynamic traffic situations, simpler control mechanisms which result in behavioural adaptation can be identified. Among these mechanisms, maintenance of safety margins and proper attention allocation play a major role. All these effects influence the end result of accident risk as separate mechanisms.
Abstract