The historic nature of most road environments has not resulted in a structurally safe traffic system. The crucial question is how potential errors occurring in traffic can be reduced by designing a road environment that is optimally adapted to the needs of road users. In order that road design measures have the desired effect on the behaviour of the driver, the road environment needs to be perceived by the driver in the way it was purposely designed. Drivers are likely to perceive those events that are in line with their expectations and will overlook events that are not in line with their expectations. The task hierarchy of driving is modelled in relation to perception of the road environment. The role of conspicuity of road elements is discussed. It is suggested that traffic signs should be clearly visible before they are readable. Studies have shown that even conspicuous signs may be ignored if not considered relevant to the task in hand. The role of expectations in the design of road elements, subjective road categorisation, and design rules for optimal highway design are explained.
Abstract