Clocks across the U.S. will be set back an hour this weekend, and one unintended consequence is that more deer will probably be struck by a vehicle next week.New research published in Current Biology found that the week after the fall time change sees an average of 16 percent more deer-vehicle collisions.How much more dangerous dusk driving will be next week depends on where you are. Counties on the eastern edge of a time zone are likely to see more deer being struck than those on the western side.
Criticisms of how the United States handles daylight saving time are about as old as the practice itself. We now have one more reason to think about not switching the clocks every six months: more roadkill.
A new study published in Current Biology by researchers from the University of Washington found that the week after the annual shift back to standard time sees a 16 percent increase in deer-vehicle collisions each year. Without falling back out of daylight saving time, the U.S. would see 36,550 fewer of these collisions—including 33 human deaths and over 2000 human injuries—and save $1.2 billion in collision costs each year, the researchers estimated. On average, around 2.1 million deer-vehicle collisions happen in the U.S. each year. These incidents are responsible for over $10 billion in economic losses as well as 59,000 human injuries and 440 human deaths.
The reason there are more collisions when the clocks fall back is relatively easy to understand. The researchers found that deer-vehicle collisions are 14 times more frequent in the two hours after sunset than before sunset. Animals, of course, stick to their pattern no matter what human clocks say, going about their lives even as traffic patterns shift to an hour “earlier” and causing more driving at dusk. Moving our clocks in November increases the amount of low-light traffic, which puts more deer and vehicles at risk. The potential for deer-vehicle interactions is already increased in November because that’s when white-tailed deer (and some other ungulates) have their short breeding season.
The study’s authors also found that there is a difference between eastern and western areas within a given time zone. Counties on the eastern edge (which have earlier sunrises and sunsets compared to the western side and a correspondingly higher amount of low-light dusk driving) had an average of 1.4 times more collisions than counties on the western side of a time zone. These findings extend to the expected changes in deer-vehicle collisions should the U.S. permanently move to daylight saving time (as the U.S. Congress is considering), with some states, like Kansas, seeing an expected 2.5 percent increase in such collisions. In comparison, Maine would see an 8.3 percent decrease.
If the U.S. got rid of biannual clock shifts and instead shifted to using only standard time, researchers estimate, deer-vehicle collisions would increase all across the country by an average of 5.2 percent, resulting in an expected additional 66 human fatalities and more than $2 billion of economic loss each year.
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