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After ‘falling back’ chances of hitting a deer jump by 16% per UW research

As the temperature drops and the days grow short, vehicle-deer collisions increase. It’s a yearly cycle driven by biology, infrastructure, hunting and the time change. Here a dead deer is seen in the Okanogan Valley.  (Jay Kehne/Conservation Northwest)
As the temperature drops and the days grow short, vehicle-deer collisions increase. It’s a yearly cycle driven by biology, infrastructure, hunting and the time change. Here a dead deer is seen in the Okanogan Valley. (Jay Kehne/Conservation Northwest)

As of Sunday, you are 16% more likely to hit a deer while driving. At least for the next few weeks.

That’s one of the findings from a University of Washington study looking at how “falling back” an hour impacts vehicle-deer collisions.

The study was published in Current Biology on Wednesday and looked at traffic accident data and insurance claims from 23 states.

The findings are stark with researchers estimating that 37,000 deer and 33 people die annually due to the switch from daylight saving to standard time in the fall.

The study also estimates the switch is responsible for 2,054 human injuries and $1.19 billion in collision costs annually. Researchers argue that adopting permanent daylight saving time, a bill that is stalled in Congress, “would yield substantial benefits for wildlife conservation and reduce the social and economic costs of deer-vehicle collisions.”

One of the lead authors, Calum Cunningham, emphasized the study is looking solely at the effect the fall time switch has on vehicle-animal collisions.

“Our paper has one argument in favor of permanent daylight saving time,” he said. “But importantly, the medical community is cautioning that daylight saving time is expected to be detrimental to human health.”

Many sleep experts believe adopting permanent daylight saving time would be bad for sleep cycles. Those experts instead urge the adoption of permanent standard time.

While Cunningham said there is “no easy answer” to the larger question, it is clear that driving is more risky during the time switch.

There are multiple reasons for that, Cunningham said.

First, deer, elk and other animals live by the rhythm of the sun, not arbitrary hands on a clock. During the fall time change the majority of traffic shifts suddenly to after sunset, a time when ungulates are most active. That abrupt change in human activity, divorced as it is from the natural rhythms of life, leads to more accidents.

“The animals don’t know anything about these time schedules,” he said.

At the same time, the fall time switch coincides with the mating season – known as the rut. During this time, deer are more aggressive and less cautious.

“The autumn time switch occurs smack dang in the middle of deer breeding season, so deer are already moving around a lot,” he said. “They’re fixated on reproducing and they’re probably not very conscious of other risks. They’re already at risk and then we add to that this increase in driving after sunset.”

There was not a similar effect in the spring time change.

“That’s pretty compelling evidence that standard time is not very good for vehicle collisions,” Cunningham said.

In Western states, the peak in vehicle-animal collisions was less pronounced, likely due to the fact that there are more mule deer in the West. Mule deer breeding seasons vary more than white-tails, Cunningham said.

“States dominated by white-tail deer have these extremely defined peak,” he said.

“Whereas the Western states, where mule deer are more predominant, they had a much more drawn-out pattern of collisions across the year.”

While the increase in vehicle-animal collisions during the fall time change has been well-documented, the UW study is the first to look at it over a number of states and analyze which time regime is best, said Tom Langen, a biologist at Clarkson University in New York who studies the environmental impacts of infrastructure. Langen was not involved in the UW study. In 2021, he published a study looking at the same question but focused solely on New York state, a study cited by the UW researchers.

“What the UW study did was try and extrapolate nationally,” he said.

He praised the UW study, particularly for its effort to estimate the economic cost of collisions, although he noted that the specific figures used might be debatable.

“The magnitude of the cost, I mean somebody could try and quibble about that, but I think the main take home message is I think they’re correct,” he said. “If you’re just looking at deer-vehicle accidents, the time change does result in significant economic costs, a significant number of injuries and an elevated number of deaths.”

The research is the newest brick in the burgeoning area of research known as road ecology, a discipline that has “started booming” in the past decade, Cunningham said. Much of that focus has been on infrastructure upgrades, primarily over- and underpass crossings such as I-90’s animal crossings near Snoqualmie Pass.

Those projects have “huge benefits,” but Cunningham said these physical upgrades need to be paired with human behavioral changes. While switching to permanent daylight saving time may not be possible – or wise – he suggested other methods such as seasonal speeding limits after dark.

“People might not love (that),” he said. “But it might also save your life.”

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