Just as a driver never knows which way a deer in the headlights will jump, a study of Highway 93’s wildlife fencing project produced some unpredicted results.
For example, the place where most deer turn into roadkill isn’t always the best place to build a crossing structure. And the usefulness of an animal underpass depends on how long we build the fence beside it.
“The fences are reducing collisions, and the crossing structures are passing animals,” said Marcel Huijser, lead author of the Montana Department of Transportation study released last November. “But there are more nuanced messages in there.
"Before the study, we thought it didn’t matter if a fence was one mile or three miles long. But that’s not true,'' he said. "We can reduce collisions 80 to 100 percent, but only if the fence is at least three miles long. If it’s shorter, the effectiveness drops to about 50 percent.”
Highway 93 has 39 wildlife crossing structures along 56 miles on the Flathead Indian Reservation between Evaro Hill and Polson. Motorists can’t miss the big overpass near the Gray Wolf Casino north of Missoula, but few realize the roadway has small, medium and large culverts tunneling underneath as well. More than 22,000 animals use those crossings every year.
The study looked at that stretch of road between 2002, when the wildlife mitigation project was under consideration, and 2015, after it had been in place for a few years. Ironically, that exposed another quirk in the results. While wildlife collisions fell by at least 50 percent in the places with fences and crossing tunnels, reported crashes actually went up for the roadway as a whole.
At the same time Highway 93 was getting its animal crossing structures at the southern end, it was getting extensive road-widening and curve-smoothing improvements to the north. That made it more likely that people would drive faster, and consequently, they hit more deer in places where fences and crossing structures weren’t in place.
Confederated Salish and Kootenai tribal biologist Whisper Camel, a co-author of the study, explained that highway safety depends on what goal gets chosen. Road engineers in Alberta’s Banff National Park focused their highway structures on protecting grizzly bears and moose from passing cars. The Flathead highway crossings tilt more toward keeping human motorists safe from animals.
“The models we did showed the forested Evaro area had a higher need for continuous fencing,” Camel said. “The more agricultural areas didn’t seem as important. But now we’re seeing deer moving through there quite frequently, and that has to do with where houses are and the population increases in the valley. Now we know that the area between Post Creek Hill and Ronan needs work.”
Whitetail deer make up the overwhelming majority of both animals hit on the roadway and animals successfully using the crossing structures. Reducing deer collisions saves human lives, car insurance expenses, law enforcement emergency response efforts and other measurable factors. However, not all benefits get tallied the same way.
“The places where we hit animals aren’t necessarily the same places where animals cross, or places where we need connectivity for wildlife,” Huijser said. “We have a lot of grizzly bear habitat close to the highway where they’re trying to cross from one mountain range to another range.”
Saving one federally protected grizzly bear or Canada lynx from roadkill can have a huge impact on the surrounding wildlife community even though it hardly makes a blip in the statistics, Huijser said.
At least 30 grizzlies have been photographed using crossing structures in the past five years. But while the $2 million overpass will most likely be the way grizzlies move from the Mission Mountains to the Bitterroot Range, far more bears get hit in the unprotected Post Hill area as they forage in valley corn fields.
Camel said finding ways to balance road safety, wildlife welfare and resident convenience will dominate future planning on the highway corridor. While the fences keep animals off the road, they also inconvenience homeowners who must open gates or maintain crossing guards on their daily travels.
“Especially where the Mission Valley is so scenic, from Ninepipes to Ronan, what happens when you put 8-foot-tall fencing along the road?” Camel asked. “Does it change the viewshed? Maybe if the highway is raised enough, no one will notice. It’s tough, and we’re not sure of the answers yet.”