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Collisions With Deer Increase at End of Daylight Saving Time

Scrapping the time change could reduce crashes, plus deaths of people and wildlife, study finds


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​We’ll get an extra hour of sleep this weekend, but it comes at a cost. Nearly 40,000 deer are struck and killed each year by drivers feeling the effects of our ritual of resetting our clocks one hour backward each fall, according to a study published in Current Biology.

As policymakers consider abandoning the twice-a-year time switch, a team of researchers at the University of Washington found that making daylight saving time year-round would reduce the carnage on our roads – likely preventing about 36,550 deer deaths, 33 human deaths and 2,054 human injuries.​

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“Wildlife-vehicle collisions are a huge and growing problem,” Calum Cunningham, a postdoctoral researcher now at the University of Tasmania, said in a statement. “There are social costs — people killed and injured — and it’s also a conservation problem as it’s one of the largest sources of human-caused mortality of wildlife.”​

There are an estimated 2.1 million deer-vehicle collisions (DVCs) in the United States each year, killing about 440 people and causing 59,000 injuries, according to the researchers.​

History of daylight saving time

​Germany implemented daylight saving time in 1916 to save fuel during World War I. The United States adopted the practice in 1918, but it wasn’t standardized across the country until the passage of the 1966 Uniform Time Act, which gave the federal government oversight of the time change. Since 2007, daylight saving time starts on the second Sunday of March, when we set our clocks one hour forward, and ends the first Sunday in November. That means that this year on Nov. 5 at 2 a.m., clocks are set back to 1 a.m.

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The practice has plenty of detractors. In recent years, increasing concerns about health effects prompted lawmakers in at least 40 states to propose legislation to eliminate the twice-yearly time changes, according to the National Conference of State Legislatures. Bills have also been filed in Congress to make daylight saving time permanent across the United States, but so far the legislation has not been enacted.​

What the researchers did

​For the study, the researchers analyzed a data set of more than 1 million DVCs in 23 states from 1994 to 2021. They found deer-vehicle collisions are more prevalent in the hours before and after sunset – when deer are more active. They found DVCs peak in the fall when deer breed. Moreover, they found a 16 percent increase in DVCs in the week following the fall shift back to standard time.​

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“We believe that this fall spike really happens due to the overlap of these two factors: the breeding season and the change from daylight saving time back to standard time. We don’t see a corresponding shift in deer-vehicle collisions in the spring during the other time change, and we believe that’s in part because spring is not a breeding season for deer,” study researcher Laura Prugh, an associate professor of quantitative wildlife sciences at the University of Washington, said in a statement.​

Based on the data, the researchers estimated an increase of 73,660 DVCs under permanent standard time, with 66 additional human deaths and 4,140 additional injuries. Making daylight saving time permanent showed the opposite trend, with a decrease of about 2.3 percent in DVCs over a full year.​

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