Study: White canvas bags better than reflectors at reducing wildlife-vehicle collisions

WORLAND - Wildlife warning reflectors and canvas bags have proven effective in reducing wildlife-vehicle collisions during a three-year study in three Wyoming counties with the most significant decrease near Thermopolis.

The Wyoming Department of Transportation and Conservation Research Center of Teton Science Schools conducted a three-year study, which concluded this spring, to evaluate the effectiveness of wildlife warning reflectors on wildlife-vehicle collisions in Big Horn, Hot Springs and Fremont counties. WYDOT installed these reflectors in 2007-2010 in several of the worst hot spots of deer-vehicle collisions in the state.

The area north of Thermopolis includes the worst single mile in Wyoming for deer-vehicle collisions, with an average of 18 per year for the last six years.

Between 2007 and 2010, WYDOT installed wildlife warning reflectors west of Riverton on 4.7 miles of U.S. 26 between Kinnear and Riverton, and just north of Kinnear; on six miles of U.S. 16/20 between Greybull and Basin; on 3.3 miles of U.S. 20 between Wind River Canyon and Thermopolis; and on 8.9 miles of U.S. 20 between Thermopolis and Lucerne.

Part of the study involved covering wildlife warning reflectors with bags to evaluate deer behavior and carcass numbers with and without the reflectors working as they are intended.

Teton Science Schools Researchers Corinna Riginos and Morgan Graham found there were 65 percent fewer deer carcasses to pick up in areas where a white canvas bag was placed over the wildlife warning reflectors, compared to areas where non-reflective black bags were placed over the posts. The wildlife warning reflectors were 32 percent more effective than black bags, but white bags were 33 percent more effective than reflectors.

"We certainly didn't expect to find something as simple as a white bag to be even more effective," said Riginos.

Riginos and Graham, in their study summary, "suggest that the white bags are more visible or reflective to deer than the red wildlife warning reflectors and are thus substantially more effective than reflectors."

Riginos said the researchers aren't exactly sure why the low-cost white bags proved more effective than the higher-cost wildlife warning reflectors. "Obviously, it's really difficult to get inside a deer's head and know exactly what they're thinking."

The red wildlife warning reflectors cost about $23.50 each, while the white bags cost about $1.50 each. "Although we recognize that white canvas bags are not a permanent mitigation solution, this price difference illustrates that a cheaper technology may exist that is more effective than the reflectors," Graham and Riginos wrote in their study summary.

Graham and Riginos believe the white bags may look like deer tails, which deer move around in "flips of white" in times of danger.

"I think it's something about the moving light, the brightness of it," Riginos said. "Even where we were doing this, the deer ultimately did cross the road when there were no cars. It just made them more aware of the vehicles and less likely to run into the road in front of a vehicle and get hit."

WYDOT plans to use the study results as a basis for continuing to improve safety on Wyoming highways for drivers and wildlife.

"Deer-vehicle collisions are also strongly associated with moderate to high traffic volumes and high speed limits of 65 mph and higher," Graham and Riginos wrote. "As traffic volumes continue to rise, deer-vehicle collisions are likely to increase as well. Limiting vehicle speeds, especially at night, may be another way to reduce collisions. On average, areas with a speed limit of 55 mph have 36 percent fewer deer-vehicle collisions than areas with a speed limit of 65 mph. This is comparable to the reductions in deer-vehicle collisions we observed in the reflector treatment areas in Thermopolis. Reducing speed limits to 55 mph at night, dawn and dusk may be an effective and much less expensive way to reduce collisions."

Riginos and Graham, in their study summary, wrote that "reducing deer-vehicle collisions in District 5 (Northwest Wyoming) and around Wyoming will likely require a suite of different strategies, some of which may be more or less suitable in different areas. These might include fencing, under- and over-passes, animal detection systems, deer vigilance-enhancing technologies, managing vehicle speed, managing roadside vegetation, and managing driver visibility and awareness. In some cases, more than one of these strategies could be combined to achieve greater effectiveness in reducing deer-vehicle collisions."

According to the study, "A simple comparison of collision rates (number per mile) before and after the reflectors were installed shows inconclusive results. In all four reflector areas, collision rates varied substantially from year to year. The Kinnear reflector area had the lowest collision rates, averaging 2.6 per mile between 2004 and 2013. Basin-Greybull had slightly higher collision rates, averaging 6.4 per mile. Collision rates were highest in north Thermopolis (13.1) south Thermopolis (15.0)."

Across all four reflector areas, there was no clear pattern of change in collision rates before and after reflectors were installed. In Kinnear, collision rates were statistically indistinguishable before and after reflector installation but with a beak high in 10 years in 2009 at about four per mile.

In Basin-Greybull, carcass rates showed a non-significant increase after the reflectors were installed. According to the study, in the 10-year comparison, Basin-Greybull had a high in 2011 of nearly 10 collisions per mile.

According to the study, "In north and south Thermopolis there was a non-significant and significant (over 2 per mile), respectively, decrease in carcass rates after the reflectors were installed. These patterns are likely a product of fluctuations in mule deer populations, perhaps in combination with effects of the reflectors."

According to the study, "These collisions pose a safety hazard and are costly; in addition to causing significant damage to vehicles and injury to their occupants, they are almost always lethal to the animal. WYDOT's estimated costs per reported collision are $11,600 in injury and property damage costs and $4,000 in restitution value (the value, in terms of lost hunter opportunity, of each killed mule deer, according to the Wyoming Game and Fish Department). Taken together, deer-vehicle collisions total approximately $24-29 million per year in Wyoming in injury and damage costs and an additional $20-23 million per year in lost wildlife value."

WYDOT Public Affairs Specialist Cody Beers said, "We're encouraged by the study that what we did was effective. We want to save human lives and the lives of the wildlife."

He added, "Vehicles are built to withstand these types of crashes and people can survive if you're buckled up." He also offered this advice. "Don't swerve to miss an animal. If you have to hit an animal do it in your lane of travel but make sure you are buckled up."