Despite the known dangers of driver fatigue, it is a difficult construct to study empirically. Different forms of task-induced fatigue may differ in their effects on driver performance and safety. Desmond and Hancock (2001) defined active and passive fatigue states that reflect different styles of workload regulation. In 2 driving simulator studies we investigated the multidimensional subjective states and safety outcomes associated with active and passive fatigue. Wind gusts were used to induce active fatigue, and full vehicle automation to induce passive fatigue. Drive duration was independently manipulated to track the development of fatigue states over time. Participants were undergraduate students. Study 1 (N = 108) focused on subjective response and associated cognitive stress processes, while Study 2 (N = 168) tested fatigue effects on vehicle control and alertness. In both studies the 2 fatigue manipulations produced different patterns of subjective response reflecting different styles of workload regulation, appraisal, and coping. Active fatigue was associated with distress, overload, and heightened coping efforts, whereas passive fatigue corresponded to large-magnitude declines in task engagement, cognitive underload, and reduced challenge appraisal. Study 2 showed that only passive fatigue reduced alertness, operationalized as speed of braking and steering responses to an emergency event. Passive fatigue also increased crash probability, but did not affect a measure of vehicle control. Findings support theories that see fatigue as an outcome of strategies for managing workload. The distinction between active and passive fatigue is important for assessment of fatigue and for evaluating automated driving systems which may induce dangerous levels of passive fatigue.

Drivers of automated vehicles may be vulnerable to fatigue that persists when normal vehicle control is restored. It is important to evaluate automated systems' impact on driver fatigue, to seek design solutions to the issue of maintaining driver engagement, and to address the vulnerabilities of fatigue-prone drivers.

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Cell phone use has been identified as a threat to driver safety. Impairments may depend on the type of cell phone usage such as calling back and text messaging. The present study investigated whether the impact of phone use depends on the state of fatigue of the driver. A manipulation of full vehicle automation was used to induce a state of passive fatigue during a simulated drive. Participants were also assigned to one of four cell phone response conditions (Cell Phone, Text Message, Free-Choice or Control). Subjective responses, vehicle control and speed of response to an emergency event were assessed. Cell phone use did not mitigate stress and fatigue produced by vehicle automation. We also replicated existing findings that phone use, especially texting, impairs normal driving performance. However, phone use during automation was associated with a faster braking response following transition to normal control, suggesting that there may be circumstances under which phone use enhances alertness. Safety implications of the findings are discussed.