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Daylight Saving Time Linked to More Deadly Car Crashes

The yearly moving-ahead of clocks in the spring may lead to more fatal car crashes throughout the U.S. during the following week, a new study has found.

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A new study out Thursday highlights a disturbing consequence of the much-hated tradition of Daylight Saving Time. It found evidence that the yearly moving-ahead of clocks in the spring leads to more fatal car crashes throughout the U.S. during the following week.

The new study, published in Current Biology, looked at federal data on fatal traffic crashes between 1996 and 2017 in states where Daylight Saving Time is observed (Hawaii and parts of Arizona excluded). They specifically focused on the week before, during, and after the time change.


Compared to those adjacent weeks, the team found there was an average 6 percent increase in the risk of a fatal car crash during the week of Daylight Saving. This increase in risk was seen even on Sunday, when many people might have the chance to sleep in. But from Monday to Friday of these weeks, the team estimated there were around five to six extra crashes a day that wouldn’t have happened if not for Daylight Saving. Across the 22-year-old study period, that would have amounted to over 600 preventable fatal accidents.

“Because the database we analyzed only includes information on the most severe car accidents, namely ones where a fatality is reported, we think it is likely that the results underestimate the risk increase in any kind of traffic accident, including minor collisions,” study author Céline Vetter, a sleep and circadian rhythm researcher at the University of Colorado Boulder, told Gizmodo via email.


As many who’ve had the misfortune of experiencing Daylight Saving likely already know, the hour ahead can make our early mornings suddenly much darker. That scenery change can muck up our body clocks, creating a smaller version of the jetlag people experience while traveling over different time zones.

This “’mini-jetlag’, together with the sleep loss that usually accompanies it, are thought to lead to fatigue and impaired cognitive function, which in turn are known predictors of accidents,” Vetter said.

The authors also noted that the changes in natural lighting during the morning and evening could affect driving conditions, though that probably plays a smaller role.

Since 2007, the U.S. has mandated that Daylight Saving—implemented originally as a way to provide people more hours of daylight and conserve energy that would have been spent lighting our buildings an extra hour in the evening—start on the second Sunday of March. Previously, it had started in April. The authors found some evidence the shift to March might have actually made fatal car crashes more likely. That said, they didn’t find evidence that the ending of Daylight Saving, now on the first Sunday of November, led to a jump in fatal accidents.


Still, coupled with other research linking the transitions in time caused by Daylight Saving to other public health risks, including an increase in heart attacks, stroke and sleep deprivation, the study is really just another nail in the coffin for ending this blasted cycle already.


“Our findings are in line with a whole body of evidence suggesting that we should abolish switching between DST and Standard Time,” Vetter said.

At least some U.S. states are starting to agree about stopping the twice-a-year time switch.


In 2019, Oregon passed a law to make Daylight Saving permanent, but it would only come into effect if Washington and California passed a similar law, to make the transition easier for everyone living on the West Coast. Washington did pass their version that same year, but it’s unclear when it might come into effect. In 2018, California residents voted to have a similar measure making Daylight Saving permanent up for approval by the state congress, but progress has since stalled.

One major debate raised by California lawmakers is over whether it’s better to get rid of Daylight Saving Time or extend it permanently. Vetter and her team’s study doesn’t provide any evidence on which system would be better. But based on other research, they do have their own preference.


“Generally speaking, there is evidence that it would be better for sleep, the body clock, and overall health to have more morning light and less evening light, as is the case if we were to adopt permanent Standard Time,” she said.

The article has been updated with comments with one of the study’s authors.