Driving in States of Fatigue or Stress

Fatigue is a serious safety problem for drivers. There are several separate sources of fatigue including sleep loss, circadian rhythm effects, and the intrinsic demands and workload of the driving task. It is important to understand both the processes that generate fatigue in the driver and the impact of fatigue states on information processing, performance, and safety. Fatigue effects involve a number of separate mechanisms and so a clear theoretical understanding of these mechanisms is needed in order to guide interventions to enhance safety. This chapter reviews methods for inducing fatigue during simulated driving, theoretical frameworks for interpreting fatigue data and practical applications. The driving simulator affords the means for controlled experiments on the interplay between fatigue and driver performance. Fatigue states are readily induced on the simulator. They may be evaluated using subjective and psychophysiological measures. The simulator also affords measurement of fatigue-induced changes in vehicle control, attention, and risk-taking behaviors. Simulator methods are also pivotal for assessment of individual differences in fatigue vulnerability, investigation of clinical fatigue conditions, and evaluation of countermeasures for fatigue. One important contribution of simulator studies is to map how environmental factors such as monotony and workload elicit fatigue responses and to track the development of fatigue states over time. Fatigue responses may be understood within the transactional theory of stress; fatigue is the outcome of a self-regulative process of managing personal discomfort and tiredness. Simulator studies have also proved valuable in testing theories of performance decrement. Studies have explored how depletion of attentional resources and breakdown of effort-regulation may contribute to driver performance impairments. Scenarios for inducing fatigue typically involve some combination of monotony and extended drive duration. High workload is not directly tied to fatigue response, but may also contribute to fatigue. Several types of dependent variables may be assessed, including measures of subjective state, psychophysiological responses, and performance data logged by the simulator.