Safety improvements and driver perception.

The paper deals with potential influences of engineering standards on driver perception. The argument is advanced that, in certain cases, the common belief that simplification of the driving task increases safety might be misleading. This might be the situation following engineering improvements. Driver confidence in the system may then be increased and driving task difficulties may be underestimated. As a result, decision criteria will be biased and driver attention level decreased. The overall effect is a degradation in driver performance which is due to a poorer detection of relevant cues and to poorer criteria. This degradation ultimately leads to an increase in accidents. The challenge of road engineering, therefore, should be to find the optimal balance between environmental demands (e.g. engineering standards and design levels) and drivers' perception of task difficulties.