The shift from daylight saving time to standard time in November is tied to an uptick in car crashes that kill more than 30 people and nearly 37,000 deer each year, according to a study published Wednesday in the journal Current Biology, adding to growing evidence that the biannual changing of the clocks is far from benign and actively harmful as a bill that would end the practice remains stalled in the House.
The shift to standard time in fall, which makes mornings brighter and evenings darker, is linked with a significant uptick in the number of vehicles colliding with deer, according to the analysis of crash data from 23 states between 1994 and 2021.
The researchers found that the number of collisions involving deer peaks in the fall, with nearly 10% of collisions happening during the two-week period around the switch from daylight saving time to standard time.
Deer and related species are most active around dawn and dusk, and the researchers found that most collisions occurred in the hours between sunset and sunrise the next morning, with incidents two hours after sunset 14 times more frequent than those two hours before.
Collisions jumped by 16% the week after the clocks changed in fall, the data showed, though the researchers did not find a commensurate shift in spring when the clocks changed back to daylight saving time again.
The pattern can be put down to changes in the deer’s behavior—fall is mating season and activity levels jump by as much as 50%—as well as more drivers after dark due to the clocks changing, the researchers said.
A year-round shift to daylight saving time would have significant benefits for deer and humans alike, the researchers proposed, potentially saving the lives of an estimated 36,550 deer and 33 humans each year, as well as preventing 2,054 human injuries and saving $1.19 billion in damages.
Across most of the U.S. this Sunday, clocks will fall back an hour and shift back to standard time. Most Americans loathe the twice-yearly change, polls suggest, but there is little unity on what system should replace it. The effects of the biannual change go well beyond inconvenience and are connected with a slew of issues including serious negative health effects like heart attacks and strokes, sleep deprivation, an uptick in fatal car crashes and huge economic losses. In March, the Senate unanimously passed legislation to put an end to the twice-yearly practice and institute permanent daylight saving time across most of the country as early as next year. The bill stalled in the House and its fate is uncertain.
2.1 million. That’s how many deer-vehicle collisions there are in the U.S. each year, according to the researchers. The vast majority of these involve two widespread species, white-tailed deer and mule deer, which are respectively more common in the eastern and western U.S. Annually, these collisions kill around 440 people, cause 59,000 injuries and cost upwards of $10 billion.
While the researchers estimate a permanent shift to daylight saving time would cut the number of deer-vehicle collisions, switching to permanent standard time would likely have the opposite effect. There would be an additional 73,660 deer-vehicle collisions under permanent standard time, 66 additional human deaths and 4,140 additional injuries, the researchers estimated, as well as an extra $2.39 billion in costs.