Implications of task-induced fatigue effects for in-vehicle countermeasures to driver fatigue.

Two driving simulator studies are reported which investigate the variation of fatigue effects with task demands and provide recommendations for system design to counteract driver fatigue. Two opposing explanations of the interactive effects of task demands and fatigue were examined. One explanation is that fatigue drains attentional resources, so that detrimental effects of fatigue on performance are accentuated when task demands increase. The alternative explanation is that fatigue disrupts matching of effort to task demands, such that the fatigued driver fails to regulate effort effectively when the task appears easy. In both studies, drivers performed both a fatiguing drive, in the first part of which they were required to perform a secondary detection task, and a control drive with no additional secondary task. In the last part of both drives, drivers were required to detect movement in pedestrian stimuli presented on both sides of the road. Vehicle control and steering movements were logged throughout both drives. The results are consistent with dynamic models of stress and sustained performance which suggest that fatigue may impair adaptation to conditions of underload, but are inconsistent with the attentional resource explanation. These task-specific fatigue effects have important implications for in-vehicle countermeasures to driver fatigue. Current approaches to the implementation of such devices fail to reflect the task-specific nature of fatigue effects. Fatigue-monitoring devices may only be valid in certain driving environments or contexts. Hence, it may be necessary to integrate performance-based feedback monitoring information with route and traffic density information from navigation systems.