DRIVER FATIGUE

Psychological fatigue is defined as a subjectively experienced disincl ination to continue performing the task at hand. It generally impairs human efficiency when individuals continue working after they have bec ome aware of their fatigue. It does not depend on energy expenditure a nd cannot be measured simply in terms of performance impairment. The i nteracting causal contributions to fatigue are the length of continuou s work spells and daily duty periods, time available for rest and cont inuous sleep, and the arrangement of duty, rest, and sleep periods wit hin each 24-h cycle. Empirical evidence for the separate and combined effects of these factors on fatigue, performance decrement, and accide nt risk are briefly reviewed, and the implications of these findings f or driving and road safety are considered, with particular reference t o the professional driver. This study shows that fatigue is insufficie ntly recognized and reported as a cause of road accidents and that its effects stem largely from prolonged and irregular working hours, rath er than simply from time spent at the wheel.