Impaired driving performance due to sleep loss is a major contributor to motor-vehicle crashes, fatalities, and serious injuries. As on-road, fully-instrumented studies of drowsy driving have largely focused on young drivers, we examined the impact of sleep loss on driving performance and physiological drowsiness in both younger and older drivers of working age. Sixteen ‘younger’ adults (M = 24.3 ± 3.1 years [21–33 years], 9 males) and seventeen ‘older’ adults (M = 57.3 ± 5.2, [50–65 years], 9 males) undertook two 2 h drives on a closed-loop track in an instrumented vehicle with a qualified instructor following (i) 8 h sleep opportunity the night prior (well-rested), and (ii) after 29-h of total sleep deprivation (TSD). Following TSD, both age groups displayed increased subjective sleepiness and lane departures (p < 0.05), with younger drivers exhibiting 7.37 × more lane departures, and 11 × greater risk of near crash events following sleep loss. While older drivers exhibited a 3.5 × more lane departures following sleep loss (p = 0.008), they did not have a significant increase in near-crash events (3/34 drives). Compared to older adults, younger adults had 3.1 × more lane departures (p = < 0.001), and more near crash events (79% versus 21%, p = 0.007). Ocular measures of drowsiness, including blink duration, number of long eye closures and PERCLOS increased following sleep loss for younger adults only (p < 0.05). These results suggest that for older working-aged adults, driving impairments observed following sleep loss may not be due to falling asleep. Future work should examine whether this is attributed to other consequences of sleep loss, such as inattention or distraction from the road.

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Study Objectives To examine whether drivers are aware of sleepiness and associated symptoms, and how subjective reports predict driving impairment and physiological drowsiness. Methods Sixteen shift workers (19-65y; 9 women) drove an instrumented vehicle for 2-hours on a closed-loop track after a night of sleep and a night of work. Subjective sleepiness/symptoms were rated every 15-minutes. Severe and moderate driving impairment was defined by emergency brake manoeuvres and lane deviations, respectively. Physiological drowsiness was defined by eye closures (Johns Drowsiness Scores, JDS) and EEG-based microsleep events. Results All subjective ratings increased post night-shift (p&lt;0.001). No severe drive events occurred without noticeable symptoms beforehand. All subjective sleepiness ratings, and specific symptoms, predicted a severe driving event occurring in the next 15-minutes (OR: 1.76-2.4, AUC&gt;0.81, p&lt;0.009), except ‘head dropping down’. KSS, ocular symptoms, difficulty keeping to center of the road, and nodding off to sleep, were associated with a lane deviation in the next 15-minutes (OR: 1.17-1.24, p&lt;0.029), although accuracy was only ‘fair’ (AUC 0.59-0.65). All sleepiness ratings predicted severe ocular-based drowsiness (OR: 1.30-2.81, p&lt;0.001), with very good-to-excellent accuracy (AUC&gt;0.8), while moderate ocular-based drowsiness was predicted with fair-to-good accuracy (AUC&gt;0.62). KSS, likelihood of falling asleep, ocular symptoms and ‘nodding off’ predicted microsleep events, with fair-to-good accuracy (AUC 0.65-0.73). Conclusions Drivers are aware of sleepiness, and many self-reported sleepiness symptoms predicted subsequent driving impairment/physiological drowsiness. Drivers should self-assess a wide range of sleepiness symptoms and stop driving when these occur to reduce the escalating risk of road crashes due to drowsiness.

Introduction Driving impairment due to sleep loss is a major contributor to motor vehicle crashes resulting in severe injury or fatalities. Ideally, drivers should be aware of their sleepiness and cease driving to reduce risk of a crash. However, there is little consensus on how accurately drivers can identify sleepiness, and how this relates to subsequent driving impairment. To examine whether drivers are aware of their sleepiness, we systematically reviewed the literature. Methods The research question for this review was “are drivers aware of sleepiness while driving, and to what extent does subjective sleepiness accurately reflect driving impairment?”. Our search strategy led to thirty-four simulated/naturalistic driving studies for review. We then extracted the relevant data. Correlational data were examined using meta-analysis, while predictive data were assessed via narrative review. Results Results showed that drivers were aware of sleepiness, and this was associated with both driving impairment and physiological drowsiness. Overall, subjective sleepiness was more strongly correlated (a) with ocular and EEG-based outcomes (rweighted = .70 and .73, respectively, p&lt;.001), rather than lane position and speed outcomes (rweighted = .46 and .49, respectively, p&lt;.001); (b) under simulated driving conditions compared to naturalistic drives; and (c) when the Karolinska Sleepiness Scale was used to measure subjective sleepiness. Lastly, high levels of sleepiness significantly predicted crash events and lane deviations. Discussion This review presents evidence that drivers are aware of sleepiness when driving, and suggests that interventions such as stopping driving when feeling ‘sleepy’ may significantly reduce crash risk.