Mountain Lions May Be Making Roads Safer, Study Finds

Mountain Lions May Be Cutting Deer-Vehicle Crashes by Up to 76% on Washington’s Olympic Peninsula

Deer-vehicle collisions kill and injure thousands of Americans every year, often when a deer darts into traffic at the worst possible moment. A new study points to an unlikely ally in cutting that risk down on Washington’s Olympic Peninsula: the mountain lion.

Research published in Current Biology found that deer-vehicle collisions dropped substantially in areas across the Peninsula where mountain lions, also called pumas, roam. Changes in deer behavior, rather than predation alone, may help explain why: scared deer appear to shift when and where they spend their time in ways that reduce their exposure to traffic.

Over a five-year period, deer and elk together accounted for 97% of wildlife-vehicle crashes on the Peninsula, with deer alone responsible for 92%. Those crashes left two people dead and more than 80 injured, racking up an estimated $14.7 million in vehicle repairs and health-related expenses. Why collisions clustered in some areas and not others pointed back to whether a mountain lion had been around lately.

Cameras and GPS Collars Tracked Mountain Lions and Deer Across the Peninsula

Researchers pulled together two sets of data. First, they used motion-triggered cameras at 503 spots across the Peninsula, set up by biologists working with tribal nations including the Lower Elwha Klallam Tribe, Makah Tribe, Quinault Indian Nation, and Skokomish Indian Tribe. Those cameras caught deer, elk, and mountain lions on film, showing who passed through and when.

Second, the team strapped GPS collars on 59 mountain lions, letting researchers see where the cats actually spent their time and how heavily they used different parts of the landscape.

For crash data, researchers pulled five years of wildlife-vehicle collision records from the Washington State Department of Transportation, covering July 2020 through June 2025 and totaling 953 crashes involving hoofed animals. They mapped the Peninsula into a grid of roughly 5-by-5-kilometer squares and compared crash rates in each square to how often mountain lions turned up nearby, focusing on the squares that had camera coverage and enough roads and deer to make a crash possible in the first place.

Deer Avoided Roads and Shifted Into Daylight Hours When Mountain Lions Were Near

In areas where mountain lions were present, deer changed their habits in two ways that both pointed toward fewer road encounters. At sites with dense road networks, deer occupancy was 15% lower when a mountain lion was nearby, a modest but real pullback rather than a mass exodus. They also holed up much farther from development, turning up 86% more often in the most remote spots when pumas were around. Developed land tends to mean more traffic, so that shift away from it may have helped keep deer out of harm’s way, though the researchers used development as a stand-in for traffic rather than measuring it directly.

Pumas hunt mostly at night, when the dark gives them an edge. Deer seem to know it. Camera footage showed deer becoming more active during the day and less active at night in areas where mountain lions were around, likely because daylight is safer. That shift matters for road safety, since drivers can spot a deer far more easily in daylight than in headlights at midnight. Crashes also tended to skew toward daytime hours where puma activity was high, though that pattern showed up more clearly in the GPS collar data than in the camera data alone.

Deer-Vehicle Collisions Dropped by Up to 76% Where Pumas Were Present

Researchers modeled how crash risk changed as mountain lion presence increased, and the pattern wasn’t a straight-line drop. In an area with moderate development, the odds of at least one crash over five years rose to a peak of 64% at moderate puma presence, then fell sharply to 21% where pumas were most active, a 67% reduction from that peak. Total expected crashes told a cleaner story: in areas with lots of deer and moderate development, the expected crash count dropped from 2.0 collisions where pumas were scarce to just 0.5 where they were most common, a 76% reduction. Both the camera data and the GPS collar data pointed to the same conclusion.

Mountain Lions May Offer a Hidden Public-Safety Benefit

Researchers are quick to point out that this kind of camera-based evidence shows a strong pattern, not ironclad proof of cause and effect. Other things that shape deer behavior, like seasonal migration and hunting by humans, weren’t fully teased apart in this study. The cameras were also concentrated in low-to-moderately developed areas, so it’s an open question whether the same effect would hold up in a dense city or suburb.

Still, the findings carry weight for debates about whether humans and large predators can share landscapes. The study ties puma presence to a real public cost, the $14.7 million in crash-related expenses mentioned earlier, though it did not calculate how much of that money pumas may have helped save.

“Coexistence with humans in a mosaic of unprotected, working, and partially developed landscapes will be crucial to facilitating the ongoing recovery and long-term persistence of large carnivores,” the authors write.

In communities where large carnivores are present or returning, residents often push back against them. This research gives that debate something concrete to chew on: living near large predators may come with a real public-safety upside, at least in landscapes like the Olympic Peninsula, a point worth weighing for transportation planners and wildlife managers alike.

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