Increased deer-vehicle collisions after time change

A study from the University of Washington found a 16 percent rise in collisions between vehicles and deer in the week after the return to standard time in the United States. The research, published in Current Biology in 2022, analyzed over a million such collisions across 23 states from 1994 to 2021.

Deer activity peaks at dusk and dawn

Deer are most active during twilight hours, making collisions more likely between sunset and sunrise. The study found that collisions are 14 times more frequent two hours after sunset than before. The species involved are primarily Virginia deer in the east and mule deer in the west.

Time change shifts traffic patterns

The biannual switch between standard time and daylight saving time creates a natural experiment by altering drivers' schedules without affecting deer behavior. After returning to standard time, the sun sets one hour earlier on the clock, but office hours remain unchanged. This shifts the evening traffic peak to after sunset, when deer are active.

Permanent daylight saving time could reduce accidents

According to the study’s model, adopting permanent daylight saving time could prevent around 36,550 deer deaths, 33 human deaths, and save $1.19 billion annually in costs. Conversely, permanent standard time would increase collisions, injuries, and costs by significant amounts. These figures are based on data from 23 U.S. states, not a nationwide count.

Debate over time policy continues

The study supports permanent daylight saving time, but lawmakers may consider other factors like health and energy use. In Europe, the return to standard time is set by a directive, with the next change happening in October 2026. The European Parliament voted in 2019 to end seasonal time changes, but no agreement has been reached on a permanent choice between daylight saving or standard time.

Risk remains under both time systems

The authors note that both permanent time options would eliminate the extra risk from the biannual time change. However, the remaining risk differs: permanent daylight saving time saves $1.19 billion annually, while permanent standard time would add $2.39 billion in costs. Drivers in areas with forested roads may benefit from slowing down during dusk hours after the time change.