The question isn’t “Why did the salamander cross the road?” It’s “Why did the salamander cross UNDER the road?”
The answer: To get to the other side without being squished by a car.
For salamanders and other amphibians, like so much wildlife, roads are no joke – not even a bad one. For creatures who migrate between the water and the surrounding forest, the effects can be particularly lethal. Each spring, adult frogs, newts and salamanders will move en masse from their wooded homes to nearby ponds and streams to mate and lay eggs. If a road lies in their path, the results are predictable.
Residents of of Monkton, a small town in the far outskirts of Vermont’s largest city, Burlington, witnessed a cruel example in the spring of 2006 on a town road that cuts between uplands and water. “They counted over a thousand dead animals on the road in just two nights,” said Brittany Mosher, an ecologist at the University of Vermont (UVM) in Burlington.
Instead of just shaking their heads and muttering about the damn traffic, locals got busy. Led by Monkton resident and state wildlife biologist Steve Parren, neighbors, state officials, university scientists and environmental groups collaborated to build a possible solution: Two 1.5 meter-wide concrete tunnels were built beneath the road, amphibious underpasses meant to give these creatures a safe route when they felt the stirrings of spring.
But would they work? That’s where this project stands out. In recent years, technical fixes to reduce road-crossing carnage have become increasingly common. That includes motion-sensitive warning lights at elk crossings and large, animal-friendly overpasses or tunnels. But the long-term outcomes often aren’t measured or only after the infrastructure is built, missing the rigor of studies comparing what happened before and after.
Not so in Monkton. There, for 12 years volunteers and UVM scientists spent rainy spring nights surveying parts of a 1.3 kilometer stretch of road to count amphibians, both alive and dead. Five years of that work happened before the underpasses opened.
Those spring forays revealed what amphibian advocates had been hoping for. In places where the tunnels and adjoining concrete “wings” were installed, the body count fell by 80%. Among amphibians that aren’t adept at climbing trees (or small concrete walls), the effect was even greater, with a 94% drop in deaths. “It was surprising. I knew that underpasses would work, but I didn’t think they would be that effective,” said Matthew Marcelino, an ecologist at UVM and lead author of a new paper describing the results in the Journal for Nature Conservation.
The tunnels, it turned out, weren’t only for frogs and salamanders. Wildlife cameras captured black bear, bobcats and porcupines crossing beneath the road as well.
That doesn’t mean the problem was completely solved. While deaths of climbing amphibians, especially tiny frogs known as spring peepers, fell by 74%, it wasn’t statistically significant. Distressingly, the total number of dead amphibians didn’t improve in buffer zones on either side of the tunnels, as well as sections of the road further from the tunnels.
The scientists have a few suggestions for tweaks that could improve performance. Angling the concrete walls further away from the road could help steer more animals toward the tunnel. Putting an overhang at the top of those walls might prevent tree climbers from scaling the walls and hopping into traffic.
But for those critters unlucky enough to not find the new infrastructure at all, the scientists don’t touch on another answer that’s cheap and involves no additional roadwork. Maybe people should just try driving their cars less often.
Marcelino, et. al. “Assessing the efficacy of wildlife underpasses in mitigating amphibian road mortality: A case study from the northeastern United States.” Journal of Nature Conservation. March 12, 2025.
Image: ©Joshua Brown / University of Vermont
