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To examine whether drivers are aware of sleepiness and associated symptoms, and how subjective reports predict driving impairment and physiological drowsiness. 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. All subjective ratings increased post night-shift (p<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>0.81, p<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<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<0.001), with very good-to-excellent accuracy (AUC>0.8), while moderate ocular-based drowsiness was predicted with fair-to-good accuracy (AUC>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). 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. |
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