Fatigue, Circadian Rhythm, and Truck Accidents

Abstract

Most truck accidents occur because of driver error, and many likely are the result of failures in vigilance performance. The truck driving task requires the driver to maintain a continual vigil if he is to perform successfully. Truck drivers often drive for long hours and at all times of the day and night, conditions that expose them to the effects of fatigue and circadian rhythms. Fatigue and circadian effects on vigilance performance are well-established. The purpose of the analyses reported here was to see if such effects were present in truck accidents which seemed to be the result of failures in vigilance performance.

Interstate truck accident data provided by the Bureau of Motor Carrier Safety of the U.S. Department of Transportation were analyzed for three groups of drivers: dozing drivers, those who had had single-vehicle accidents, and those who had crashed into the rear end of other vehicles. The effect of fatigue was confirmed for each of the groups: Fewer accidents than expected occurred early in trips and more than expected later in trips; about twice as many accidents occurred during the second half of trips than during the first half, irrespective of trip duration. The circadian effect was observed for dozing drivers, about twice as many of whose accidents occurred between midnight and 0800 hours than in the other 16 hours of the day, and for single-vehicle accident drivers, about half of whose accidents occurred in the early morning hours. The circadian effect was not as marked for drivers having accidents involving a second vehicle, likely because of variations by time-of-day in the number of vehicles on the road.

There is some evidence of a combined effect of fatigue and circadian rhythm on the relative likelihood of occurrence of accidents.