A Straight Dope Classic from Cecil's Storehouse of Human Knowledge

Does Daylight Saving Time increase road kill?

April 13, 2012

Dear Cecil:

On my drive into work today, the first workday back since the Daylight Saving Time spring forward, I noticed a stark increase in road kill, specifically raccoons. Has anyone else noticed this? My theory is it has to do with more drivers on the street before sunrise because of the hour shift forward.

Cecil replies:

There are indications — but so far no proof — that the Daylight Saving Time (DST) change imperils the gentle creatures of the woodland. But some say Bambi, Thumper, and Rocky aren’t the real concern. The mammal more clearly in danger of getting turned into road kill is you.

DST began as a joke. In a satirical piece published anonymously in 1784, Benjamin Franklin, then living in Paris, claimed to have recently discovered that the sun begins shining early each morning — roughly six hours, in fact, before he typically got out of bed. He then calculated the vast savings on candles that would accrue to his fellow Parisians if they all got up at sunrise, and proposed to encourage this practice by, among other things, firing off cannons at dawn.

Ever the cutup, that Ben. In 1895 the pioneering New Zealand naturalist and astronomer George Vernon Hudson came up with a more practical solution: changing the clocks. In the U.S., DST was first tried as a nationwide wartime conservation measure in 1918, then again in 1942, and finally became the norm in 1966. Subsequent congressional tinkering ultimately produced our current system of starting on the second Sunday in March and ending on the first Sunday in November.

Many animals are either nocturnal or crepuscular (i.e., active at twilight — and trust me, your date will be impressed when you work that word into a sentence). So it’s conceivable that an abrupt shift in traffic volume at dusk and dawn could affect the frequency of auto-animal encounters. A study of more than 21,000 crashes between car and deer (mostly moose and white-tails) in Finland found a very high peak in such accidents from 30 to 120 minutes after sunset, with a much smaller peak about half an hour before sunrise.

We also know that the times of year we time-shift for DST — spring and fall — align to an extent with road-kill peaks for some animals. For example, deer typically have two peak road-kill periods. One is in May and June, which I grant you is quite a bit after the DST shift. But the other is in October and early November, right around the change, and is much larger than the spring peak.

Coincidence? Hard to say. Despite several large-scale multistate investigations, there’s no smoking gun tying DST to more (or fewer) animals killed on the roads.

DST’s effect on humans has been more carefully scrutinized, and a few researchers claim to have found evidence the time change can be dangerous. The loss of an hour of sleep time in the spring is thought, not unreasonably, to be especially rough, leading to more accidents on the road and in the workplace. Conversely, some hypothesize that an extra hour of sleep in the fall should translate into a reduction in accidents.

You can find research supporting this premise. For example, a Canadian study of nearly 22,000 auto accidents around DST change days claimed that accidents increased by 8 percent immediately after the spring forward, and decreased by 7 percent immediately after the fall backward. But that study looked at just two years. A skeptic examining ten years’ worth of data from the same source found no important difference.

From what I can see, that’s the general rule with time-change research. For every study claiming to show DST kills, you can come up with another saying it’s harmless — in my book a pretty good indication the apparent patterns in the data are just a fluke.


Dear Cecil:

Just one quick, simple question: can the indoctrination into a region at an early age cause brain damage?

Cecil replies:

No, but it wreaks havoc with your ability to spell.

Dear Cecil:

In a morgue, where would the toe-tag be placed on a footless or legless body? One step beyond that: where would it be placed on a torso with no arms or legs or if even the head was missing?

Cecil replies:

One assumes one would assess the appendages available, and do the best one could.

Dear Cecil:

Does your wife ever win an argument with you? Not a "Where are the car keys?" argument — an actual physical-universe, semi-scientific, Wheel of Fortune-type argument.

Cecil replies:

Wheel of Fortune” and “semi-scientific” aren’t expressions you expect to see in the same sentence. However, I assume what you’re getting at is whether I win spousal arguments admitting of factual resolution. All I can say is: you’ve obviously never been married, sport.


Related Posts with Thumbnails


Aldridge, A.O. “Franklin's Essay on Daylight Saving” American Literature 28.1 (Mar., 1956): 23-29.

Barnes, Christopher M. and Wagner, David T. “Changing to Daylight Saving Time Cuts Into Sleep and Increases Workplace Injuries” Journal of Applied Psychology 94.5 (2009): 1305–1317.

California Roadkill Observation System. Performance Report, August, 2010. University of California, Davis.

Coren, Stanley “Daylight Savings Time and Traffic Accidents” New England Journal of Medicine 334.14 (4 April, 1996): 924.

Haikonen, Hannu and Summala, Heikki. “Deer–Vehicle Crashes Extensive Peak at 1 Hour After Sunset” American Journal of Preventive Medicine 21.3 (2001): 209-213.

Lahti, Tuuli et al. “Daylight Saving Time Transitions and Road Traffic Accidents” Journal of Environmental and Public Health (2010): 1-5.

Lahti, T. et al. “Work-related accidents and daylight saving time in Finland” Occupational Medicine 61 (2011): 26–28.

Lambe, Mats and Cummings, Peter. “The shift to and from daylight savings time and motor vehicle crashes” Accident Analysis and Prevention 32 (2000): 609–611.

Shao, Chun et al. “High and Low Deer-Vehicle Collision Roadway Sections - What Makes Them Different?” The Open Transportation Journal 4 (2010): 87-92.

Varughese, Jason and Allen, Richard P. “Fatal accidents following changes in daylight savings time: the American experience” Sleep Medicine 2 (2001): 31-36

Vincent, Alex “Effect of Daylight Savings Time on Collision Rates” New England Journal of Medicine 339.16 (15 October, 1998): 1167-1168.

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