PERCEPTION OF HIGHWAY TRAFFIC SIGNS

A review of laboratory and field studies relevant to determining the effectiveness of traffic signs is presented. The laboratory studies discussed concern the number of signs which can be perceived simultaneously and the effect of conspicuity on perception during a short period of exposure. Conspicuousness of signs depended on the brightness, brightness contrast, and visual simplicity-complexity dimension of the signs. Results of two field studies examining various factors affecting the mental registration of traffic signs revealed that only signs with a high signal value reach the driver's consciousness so that he can make a decision as to whether he has to alter his action. Three factors which seem to affect the signal value of a traffic sign include: 1) the size of the risk to which, according to the driver's experience, he, the passengers, the vehicle, and other road users are exposed, 2) the probability of which disobediance of the signs is followed by punishment, and 3) the customs and norms assumed by the various groups of road users (e.g., private vs. professional license holders). Results of a study determining the effect of police supervision on the perception of traffic signs revealed that the perception probability of a traffic sign was reduced when a patrol car parked near the sign but grew when the patrol car was parked sufficiently far ahead of the sign. /PB/