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Shift-work puts workers at heightened risk of heart disease and obesity, among other chronic diseases. It also puts everyone else at risk of being run off the road by a runaway Camry. A new study, from Brigham and Women’s Hospital, published in the Proceedings of the National Academy of Sciences, found that daytime driving performance of shift-workers suffers considerably when they’ve spent the night on the job, rather than in their beds.

For the study, shift-workers completed daytime test drives shifts, both after spending a night working and sleeping, respectively. Sixteen participants performed two-hour driving sessions at a closed-off track. Before one session, they got a solid night of rest, average 7.6 hours. Before the other session, they labored until sun-up. Researchers evaluated performance based on three unsafe driving behaviors: near-crash events, terminated drives due to loss of control and lane-weaving.

They also looked at physiological gages of tiredness. They used EEG to measure micro-sleep episodes (sleep for less than three seconds) and monitored partial eyelid closure with slow-eye movements, which indicate the transition between sleep and wakefulness. Speaking on behalf of everyone who uses America’s roadways, people toiling on the cusp of unconsciousness should not climb behind the wheel.

After spending the night working, more than a third of participants were involved in near-crash events. Nearly half of participants lost control and had to terminate their drives. Across the board, post-work drivers had a much higher rate of lane-swerving and exhibited the drawn-out blinking and slow-eye movements indicative of not-quite being awake. And the risk of micro-sleeps shot up at the half-hour mark.

The results, according to a press release, show an increased risk of car accidents related directly to drowsy driving. "These findings help to explain why night shift workers have so many more motor vehicle crashes than day workers, particularly during the commute home,” said Charles Czeisler, study co-author and chief of Division of Sleep and Circadian Disorders at Brigham Young, in the press release. “Night shift workers should be advised of the hazards of drowsy driving and seek alternate forms of transportation after night shift work."

The study wasn’t without limitations. Drivers, for instance, were aware of their participation in a study on impaired performance and shift work, and they (thankfully) weren’t navigating rush hour on the open road. It’s possible they’d perform differently in a real-word scenario, although the considerable discrepancy between their performance in the two sessions gives us enough pause to avoid drowsy driving. Nothing says holiday cheer like a rogue minivan.