Early Sunday morning, clocks in 49 states sprang forward and many Americans “lost” an hour that they probably would have spent asleep. And then today millions of slightly drowsier-than-normal drivers hit the nation’s roadways and headed to work.

Researchers have been skeptical about whether clock-shifting schemes achieve their original stated purpose of saving fuel, with one study finding evidence that daylight saving time actually increased household energy use in Indiana after a policy switch. Regardless of any energy savings, the disruption inherent in springing forward could come with additional costs.

U.S. government surveys show that on the Sunday in March marking the beginning of DST, the average American sleeps 40 minutes less than usual. In an article appearing last spring in the American Economic Journal: Applied Economics, Austin Smith probes the connection between reduced sleep, changing light conditions, and motor vehicle accidents.

Figure 7 from Smith (2016)

The dangers of driving while tired are well known to experts, but might be underappreciated by most drivers. Smith finds that fatal accidents are slightly but significantly elevated in the week after the daylight saving time sleep disruption, resulting in approximately 30 additional deaths on American roads each March (see figure above).

These findings raise questions about the potential costs of other events and technologies that lead to sleep loss – and underscore the importance of catching up on sleep before getting behind the wheel. “Moving the transition date back a day, to early Saturday morning” could help provide people more time to adjust before the workweek starts, says Smith. “That, in conjunction with PSAs about drowsy driving, could make a dent.”