In a driving simulator the effects of time-on-task were measured on variables that measure drowsiness, driving performance and steering behaviour for groups of younger and older drivers. It was found that the fraction of time during which the eyes were closed is a good measure of drowsiness that is sensitive to the effects of time-on-task. Of all single variables that measure driver performance and impairment, the percentage of time during which any part of the vehicle exceeded one of the lane boundaries was the most strongly affected by time-on-task. Also, with progressing drowsiness, the amplitude of steering corrections increased towards larger values. This was caused both by larger error corrections in response to larger errors and by an increase in coarseness of the steering response. Large steering corrections proved to be the single best indicator of progressing impairment by drowsiness and fatigue. Older drivers performed poorer on lateral control of the vehicle compared to younger drivers. Also, driving performance of older drivers deteriorated more with time-on-task compared to younger drivers. However, there were no differences between younger and older drivers in the reliability and validity of the different measures for drowsiness, steering behaviour and driving performance. (A)
Abstract