Does Daylight Savings Time Increase Car Accidents?

A new study published in the scientific journal Current Biology finds that the spring transition to Daylight Savings Time may result in an increase in fatal car accidents in the US. The study’s authors include Josef Fritz, Kenneth P. Wright Jr., and Céline Vetter of the University of Colorado, and Trang VoPham of the Fred Hutchinson Cancer Research Center.

The study, published in January 2020, found evidence that the springtime Daylight Savings Time shift “acutely increases motor vehicle accident (MVA) risk,” a phenomenon that “has been partly attributed to sleep deprivation and circadian misalignment.” Its summary, available via Current Biology, states that the shift one-hour forward results in darker mornings and brighter evenings, which change “illumination conditions for peak traffic density,” which may reduce MVA risk in accidents and evenings.

Another factor identified in the study is the changing sunrise and sunset depending on where you are geographically in your time zone. “The sun rises at an earlier clock time in the eastern regions of a given time zone than in the western regions, which is thought to induce higher levels of circadian misalignment in the west than in the east,” the study says. This phenomenon is known as “time zone effect.”

According to its summary, the study examined “large US registry data, including 732,835 fatal MVAs recorded across all states” between 1996 and 2017, finding that the spring DST shift “significantly increased fatal MVA risk by 6%.” These changes were “more pronounced” in the morning, according to the study, and in the westernmost parts of a time zone, where the sun rises latest.

According to the study’s authors, the Daylight Savings Time-associated risk of traffic accidents rose in the afternoon, “despite longer hours,” and “waned in the week subsequent” to he shift. The study found no consequences of the autumn shift to standard time, “further supporting the hypothesis that DST-transition-associated, preventable circadian misalignment and sleep deprivation might underlie MVA risk increases.”

A New York Times report on the study noted that the increase in the risk of motor vehicle accidents “averaged 9 percent in the hours before noon,” suggesting that the phenomenon may be associated with fatigue, as well as the darker mornings. In a statement to the Times, one of the study’s authors, Céline Vetter, said: “There is strong evidence for something real going on… and there are no real benefits in daylight saving time for economics or energy saving. Let’s get rid of the switch to daylight saving time.”

The study is accessible via Current Biology.

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