TIME OF DAY VARIATIONS IN DRIVING PERFORMANCE

Numerous factors may contribute to the 24-hour pattern of automobile a ccidents. One factor may be a time of day variation in driving ability . In the present study, 11 male subjects operated a driving simulator for 30 minutes at six times of day. Subjects were instructed to mainta in a stable position in the left-hand lane and to drive at a constant speed of 80 km/hour. In addition subjects performed a secondary reacti on time task. Subjective mood was measured at the beginning and end of each session. Driving performance was measured in terms of the mean a nd standard deviation of lateral position and speed. The mean and stan dard deviation of speed varied significantly across the day for both c urved and straight segments. Reaction time was also affected by time o f day. Performance was more impaired at 0600 and 0200 hours, with impr ovements in driving performance between 1000 and 2200 hours and an ear ly afternoon dip. These results suggest that driving performance is su bject to diurnal variations. Of particular importance is the result th at impairments in driving performance in the early afternoon are of a similar magnitude to those occurring in the late evening and early mor ning. (C) 1997 Elsevier Science Ltd.