Millions of animals are killed by oncoming vehicles each year. To understand the problem, U.S. government researchers drove toward the animals in a pickup truck. No mammals, two- or four-legged, were harmed over the course of the study.
By driving toward deer on the road's edge, the scientists found that the animals were frequently slow to react, regardless of the vehicle's speed (which ranged from about 12 mph to a maximum of 55 mph).
Just after nightfall, researchers with the U.S. Animal and Plant Health Inspection Service and the Department of Wildlife drove along roads that cut through suburban deer habitat in Erie County, Ohio. The scientists' Ford F250 pickup truck was outfitted with an infrared camera that could detect deer a half mile away, minimizing the risk to wildlife by making sure each approach toward a roadside animal involved a single deer at a safe distance.
Unlike what the researchers had predicted, the velocity of the approaching truck had little impact on the deers' flight response. Between the springs of 2012 and 2013, the scientists drove toward 67 deer. Three-quarters of the deer fled the truck within 600 feet; on average, the extrapolated "time-to-collision" was only 4.6 seconds.
Animal-vehicle collisions are an unfortunate conflux of physics, bright lights and biology. It's questionable, the scientists write in the journal PLOS ONE, "whether deer or other animals can adequately process visual stimuli associated with vehicle approach." They point to a 2004 study that indicates wolves have trouble perceiving vehicles in motion, as cars don't change "body motion," like moving legs, when traveling faster or slower.
Crashing into deer is a serious problem in the U.S., accounting for 200 human deaths. It's also an expensive one, with an estimated $4 billion price tag per year. As far as wildlife fatalities go, the numbers are less clear, but the Federal Highway Administration says annual vertebrate deaths - that's mammals, reptiles, birds and amphibians - number in the millions. An estimated 17,300 animals are killed each year on British Columbia roads alone, according to a Defenders of Wildlife report.
To lessen the chance of deer collisions, there are a few ways roads could be improved, the U.S. scientists say: lowering speed limits (or signs with recommended lower speeds for given conditions) and changing traffic structure, by adding, for instance, speed bumps.