ANN ARBOR, MI --- Animal-vehicle collisions have increased 110 percent in the United States during the past 18 years, according to a new report from the University of Michigan Transportation Research Institute. 

John M. Sullivan, a UMTRI assistant research scientist, examined daily and seasonal animal-vehicle crash trends and the interaction of vehicle speed and ambient light to find out what factors influence crash risk. 

According to the report, Relationships Between Lighting and Animal-Vehicle Collisions, there were 106 traffic fatalities in the United States resulting from animal-vehicle collisions in 1990. By 2007, that level had risen to 223. Texas, Wisconsin, Pennsylvania, Ohio and Michigan are the leading states in absolute numbers of fatal animal-vehicle collisions. 

"While the exact reason for the increase is unclear, it does seem to exceed what would be expected from increases in annual vehicle miles driven or changes in the balance of rural versus urban driving," said Sullivan. "One possibility is that increases in deer population or movement patterns may be involved." 

According to the report, about 77 percent of animal-vehicle collisions involve deer. In Michigan, most animal-vehicle collisions occur in October and November, coinciding with mating season of the white-tailed deer population. The highest collision risk occurs around dawn and dusk when deer are active and ambient light levels are low. 

Using data from the Fatality Analysis Reporting System (FARS), Sullivan analyzed the influence of posted speed limits on the odds of a fatal animal-vehicle collision occurring in darkness. Modeling two ambient lighting conditions (light and dark), Sullivan found that for every mile-per-hour increase in speed, there was an increase in the odds of a crash occurring in darkness of about 2.5 percent. 

The report indicates that the relative risk of animal-vehicle collisions in darkness versus daylight appears to be associated with posted speed limit. Higher posted speeds result in proportionally greater crash risk in darkness. The take-home message for drivers, said Sullivan, is straightforward: slow down. 

"The difference between a fatal and a nonfatal crash is often a matter of impact force," explained Sullivan. Slowing down on the roadways around dawn and dusk, when deer are most active, is one of the most important actions that drivers can take to avoid a fatal collision, even if the collision itself is unavoidable. 

Another potential remedy is extending "forward preview time," or the distance a driver can see in darkness. Methods might include dynamic modification of the forward headlight beam pattern to extend a driver's view of the road, use of night vision enhancement, or use of other advanced detection systems. 

The research was sponsored by the University of Michigan Industry Affiliation Program for Human Factors in Transportation Safety.