The risk of fatal car crashes goes up in the week after the shift to summer time, or daylight saving time, each spring. In the US alone, researchers predict that about 29 deadly accidents in the week after the transition could be prevented each year.
鈥淭he best option, not only for traffic accident risk, but also health and well-being in general, would be to get rid of daylight saving time transitions altogether,鈥� says C茅line Vetter at the University of Colorado Boulder.
Vetter and her team analysed reports of fatal accidents over 22 years, from 1996 to 2017, across the US states that observe daylight saving time 鈥� which is all of them apart from Arizona and Hawaii. They compared the number of fatal traffic accidents for each week of the year with those in the week following a daylight saving time clock change, adjusting for other factors such as traffic volume, changes in car safety over the years and seasonal variation.
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They found that the risk of fatal vehicle accidents increases by approximately 6 per cent in the week following the transition.
The clock change happens on a Sunday, with the biggest effects in the following week. There were, on average, an additional 5.7 fatal accidents per day from Monday to Friday after a daylight saving time transition 鈥� or 28.5 more fatal accidents during the whole working week.
Sudden time changes disrupt our internal body clocks, leading to sleep deprivation that affects alertness, well-being and mood, says Vetter. Beyond the first week after the transition, the number of accidents returned to levels seen before the change, suggesting that people鈥檚 body clocks have adjusted by this point.
Till Roenneberg at Ludwig Maximilian University of Munich in Germany, who wasn鈥檛 involved in the study, says the results are 鈥渆xcellent evidence鈥� for the short-term effects of the switch to daylight saving time.
The study also revealed that the risk increase is highest in the morning and is more pronounced in western regions of time zones. The further west people live in a time zone, the greater the discrepancy between the clock reading noon and the sun reaching its highest point in the sky.
That can lead to larger negative impacts of daylight saving time, says Roenneberg. This may explain why the study found little impact of the clock change in the autumn, as returning to standard time brings clocks more in line with solar noon.
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