Crash risk and sleepiness during a simulated commute decrease over a week of night work

Introduction : Shiftworkers are much more likely to have a crash driving home after a night shift than other drivers on the road at the same time of day. The aim of this study was to examine the likelihood of crashing during the post- work commute at the start, middle, and end of a week of night shifts. Given that prior wake is longest at the end of the first night shift compared to the others, it was hypoth-esised that the likelihood of crashing would be greatest at the start of the week of night shifts. Methods : So far, 43 adults (21F, 22M) have completed a laboratory- based simulated shiftwork protocol with seven consecutive 8- h night shifts (23:00–07:00 hr). Participants had 9 hr in bed on the night prior to the first night shift, then they had 7 hr in bed in the breaks between each night shift. Participants had a 20- min commute before (22:30 hr) and after (07:10 hr) each night shift in a driving simulator (York Computer Technologies). Subjective sleepiness was assessed immediately prior to each commute using the Karolinska Sleepiness Scale (KSS). Results : Compared to the corresponding pre- work commute, par-ticipants were 8.2, 5.7, and 3.0 times more likely to crash during the post- work commute on nights 1, 4, and 7, respectively. Repeated- measures ANOVA indicated a significant night x commute time interaction in the subjective sleepiness data (F = 10.9; df = 2,84; p < .0001). In particular, the KSS score was similar for the pre- work commutes each night (night 1 = 3.7 ± 1.3; night 4 = 3.6 ± 1.4; night 7 = 3.7 ± 1.6), but it progressively decreased for the post- work com-mutes throughout the week (night 1 = 8.1 ± 1.1; night 4 = 7.6 ± 1.6; night 7 = 6.9 ± 1.9). Discussion : These data indicate that crash risk and subjective sleepi-ness are both relatively high during the morning commute after a night shift, but they progressively decline throughout a week of sustained night work. If generalisable to shiftworkers, the results suggest that longer sequences of night shifts may have an advan-tage over shorter sequences, in terms of exposure to crash risk while commuting.