Another Problem With Daylight Saving Time: Increased Risk of Hitting Deer on the Road

Deer in Headlights

Deer are responsible for over 1 million motor vehicle accidents in the U.S. annually, leading to more than $1 billion in property damage, approximately 200 human fatalities, and 29,000 serious injuries.

Daylight saving time ends in the U.S. and Canada on November 7, 2021, and most of us will be setting our clocks back an hour. There is a long-running debate about the benefit of the time change, given how it disrupts humans’ circadian rhythms, causing short-term stress and fatigue.

Another risk accompanying the time change is on the roads: As more people drive at dusk during an active time of year for deer, the number of deer-vehicle accidents rises.

Deer cause over 1 million motor vehicle accidents in the U.S. each year, resulting in more than US$1 billion in property damage, about 200 human deaths, and 29,000 serious injuries. Property damage insurance claims average around $2,600 per accident, and the overall average cost, including severe injuries or death, is over $6,000.

Deer Crossing Road

The likelihood of hitting a deer is highest during morning and evening twilight.

While avoiding deer – as well as moose, elk, and other hoofed animals, known as ungulates – can seem impossible if you’re driving in rural areas, there are certain times and places that are most hazardous, and so warrant extra caution.

Transportation agencies, working with scientists, have been developing ways to predict where deer and other ungulates enter roads so they can post warning signs or install fencing or wildlife passages under or over the roadway. Just as important is knowing when these accidents occur.

My former students Victor Colino-Rabanal, Nimanthi Abeyrathna, and I have analyzed over 86,000 deer-vehicle collisions involving white-tailed deer in New York state using police records over a three-year period. Here’s what our research and other studies show about timing and risk.

Time of day, month, and year matters

The risk of hitting a deer varies by time of day, day of the week, the monthly lunar cycle and seasons of the year.

These accident cycles are partly a function of driver behavior – they are highest when traffic is heavy, drivers are least alert and driving conditions are poorest for spotting animals. They are also affected by deer behavior. Not infrequently, deer-vehicle accidents involve multiple vehicles, as startled drivers swerve to miss a deer and collide with a vehicle in another lane, or they slam on the brakes and are rear-ended by the vehicle behind.

Deer Crossing Sign

A sign warns of deer traffic.

In analyzing thousands of deer-vehicle collisions, we found that these accidents occur most frequently at dusk and dawn, when deer are most active and drivers’ ability to spot them is the poorest. Only about 20% of accidents occur during daylight hours. Deer-vehicle accidents are eight times more frequent per hour of dusk than daylight, and four times more frequent at dusk than after nightfall.

During the week, accidents occur most frequently on days that have the most drivers on the road at dawn or dusk, so they are associated with work commuter driving patterns and social factors such as Friday “date night” traffic.

Over the span of a month, the most deer-vehicle accidents occur during the full moon, and at the time of night that the moon is brightest. Deer move greater distances from cover and are more likely to enter roadways when there is more illumination at night. The pattern holds for deer and other ungulates in both North America and Europe.

Vehicle Crashes Involving Deer

Over a year, by far the highest numbers of deer-vehicle accidents are in autumn, and particularly during the rut, when bucks search and compete to mate with does. In New York state, the peak number of deer-vehicle accidents occurs in the last week of October and first weeks of November. There are over four times as many deer-vehicle accidents during that period as during spring. Moose-vehicle accidents show a similar pattern.

The problem with daylight saving time

We have also found that the daylight saving time clock shift of one hour affects the number of deer-vehicle accidents.

In spring, when deer-vehicle accidents are at an annual low, the start of daylight saving time means a later sunrise and sunset. It results in a small decrease in deer-vehicle accidents. However, in fall, when deer-vehicle accidents are at an annual high because of deer rut, the earlier sunrise and sunset cause a significant increase in deer-vehicle accidents.

The clock shift results in more commuters on the road during the high-risk dusk hours. The consequence is more cars driving at the peak time of day and during the peak time of the year for deer-vehicle accidents. The clock shift results in a 37% reduction in deer-vehicle accidents during morning commuter hours, since fewer commuters are on the road before sunrise, but a 72% increase in accidents during evening commuter hours. Overall, there is a 19% increase in accidents during commuter hours the week after the fall time change in New York.

Deer still cross roads at any time

It’s important to remember that deer-vehicle accidents can occur at any time of day or night, on any day of the year – and that deer can show up in urban areas as well as rural ones.

The insurance company State Farm found that on average, U.S. drivers have a 1 in 116 chance of hitting an animal, with much higher rates in states such as West Virginia, Montana and Pennsylvania. Over the 12 months ended in June 2020, State Farm counted 1.9 million insurance claims for collisions with wildlife nationwide. Around 90% of those involved deer.

Where deer or other ungulates are likely to be present, drivers should always be alert and cautious, especially at dawn, dusk, on bright moonlit nights and during the fall rut. In addition, drivers should be aware that after the fall time change, they may be more fatigued, and their evening commute from work may have shifted into the dusk hours, when risk of hitting a deer is highest, and coinciding with the rut, when the risk is at its annual peak.

Written by Tom Langen, Professor of Biology, Clarkson University.

Adapted from an article originally published on The Conversation.The Conversation

3 Comments on "Another Problem With Daylight Saving Time: Increased Risk of Hitting Deer on the Road"

  1. stephen schaffer | November 7, 2021 at 7:14 am | Reply

    Deer are vectors for Lyme disease and now Covid. Turn them all into road pizza.

  2. Sekar Vedaraman | November 7, 2021 at 1:50 pm | Reply


    Sharing some thoughts. ⬇️

    Connect with earlier report about 80% of Deer testing positive for Covid 19 Virus and the possibility that they may be reservoir of the Virus. Where they go for R and R and come back as new VoC.

    Different creatures have different ecosystems and the fact that they are not dying in large numbers ,indicates ability to survive the infection and may give us answers and clues on how to strengthen the human ecosystem against the Virus for the long term.

    Maybe Deer are already endemic and the fact that 80 percent of Deer Population are covid 19 postive but unaffected us interesting.

  3. How fast were those people driving? Perhaps we should go back to lower speed limits at night.
    We should get rid of daylight savings time. It causes heart attacks. Big business lackeys get paid to convince you that somehow you need an extra hour of heat stroke sunlight to mow your grass. Our children have missed the experience of seeing the gradual change as the earth orbits the sun tilting on its axis. You lackeys have forgotten that the days get even longer in the north. Right now we in the south have to spend more on cooling because it somehow benefits a few corporations. 330 million should not have to change since we can’t even show a valid reason for it.

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