How fixing roadside curbs can help reptiles and amphibians survive

It was in the 1980s when Scott Jackson first encountered salamanders trapped by roadside curbs – and realized these construction features could pose a threat to animals. He was studying for a master’s degree in wildlife biology at the time, and a colleague was concerned that a recently built subdivision next to a vernal pool – a temporary wetland vital to creatures like salamanders and turtles – could be impacting local wildlife. The two visited the site and Jackson noticed vertical curbs lining both sides of the road. He looked into the catch basins on the road. Stuck at the bottom were about two dozen salamanders. The pair pulled the grates off and released the salamanders into the vernal pool. That group of salamanders was saved – but by a quick fix, not a long-term solution.

Curbs like these are a mundane feature of urban and suburban life that most of us (at least, those who don’t depend on wheels) skip over without a second thought. But for a tiny turtle hatchling or salamander trying to cross a roadway, a 90-degree angled curb can be a giant, unpassable barrier. Unable to get off the road, these animals are more likely to be hit by cars or snatched by predators, to fall into catch basins or even die by drying out. Thankfully, the solution is often straightforward: change the angle of the curb. Although it’s impossible to undo the impacts of all the roads cutting through wildlife habitat, we can ever-so-slightly rewild our roads to make them more natural for animals to cross.

Researching herps on the road

Roads pose a massive threat to wildlife. It’s thought that cars kill one million vertebrate animals in the U.S. every day, and even that could be vastly underestimated.

Reptiles and amphibians are particularly at risk. Small and slow-moving, they can take a long time to cross roads. And unlike the deer and other mammals we often associate with roadkill, they’re a lot harder for drivers to detect.

Many reptiles and amphibians also move seasonally between water and land to breed, nest and overwinter. Female turtles, for example, can travel miles looking for a nesting site. After birth, the hatchlings travel from land to bodies of water. Amphibians migrate in massive numbers to vernal pools in early spring. After years of human expansion, wild animals are increasingly being forced to cross roads for these activities.

In addition, turtles have low reproductive rates, so “even the death of a small number of reproductive adults can be devastating for a population,” says Thomas Hossie, an assistant professor of biology at Trent University in Peterborough, Ontario.

For salamanders, road mortality rates as low as 10 percent can drive local populations to extinction, says Hossie. One study in Massachusetts found that more than a third of salamanders who traveled 500 metres from their breeding pools were killed on roads.

Any road that cuts through amphibian and reptile habitat poses a threat, whether it has no curbs, sloped curbs or vertical curbs. But vertical curbs extend the amount of time an animal spends on the road, increasing its chances of dying.

Not all reptiles and amphibians are affected equally. Frogs can hop over curbs and larger turtles can climb over them. But even these animals may instead choose to walk alongside the curb looking for an exit, which can lead them straight into catch basins, says Jackson, now a professor at the University of Massachusetts Amherst specializing in reptiles and amphibians. One study estimates that up to half a million adult amphibians die after falling into catch basins in the Netherlands alone each year. The authors note that “many times this number” of young amphibians likely die this way, too.

Reptile and amphibian road mortality is receiving growing recognition, but the role curbs play is still frequently overlooked. Jackson thinks it’s because “a lot of that mortality happens down in the catch basin, so nobody even knows that it happened. It’s a less visible problem so it doesn’t come up very often.”

The Minneapolis Park and Recreation Board in Minneapolis, Minnesota, began studying turtles in the city after staff noticed a lot of reports of dead and nesting turtles near roadways. In 2021, research found that road mortality was the greatest threat the city’s turtles faced. The report outlined hot spots where turtles were getting hit by cars – and almost all the high-risk roads had vertical curbs.

Curb appeal

Vertical curbs are used for both practical reasons and aesthetic value.

Vertical curbs direct water off roads in the same way that they can funnel small critters into catch basins. On rural roads, curbs are less common because water can usually run off the shoulder and absorb into the ground. “When you get into more densely populated areas, you really need to control the runoff more carefully,” says Jackson. “There’s a lot more impervious surfaces.”

Urban and suburban neighbourhoods are full of concrete sidewalks, bisecting roads, parking lots, driveways and very little vegetation that can naturally absorb excess water. Vertical curbs are also touted as a safety measure that makes it harder for veering cars to mount them.

Vertical curbs, particularly ones made of sleek granite, serve another purpose, too: They appease our desire for sophisticated, well-designed neighbourhoods. “In these new developments in rural areas that are actually fragmenting habitats that are important to amphibians and reptiles, they’re starting to put in these curbs,” says Dennis Quinn, a Connecticut herpetologist who has consulted on multiple road mortality mitigation projects. “[It’s] for curb appeal.”

Humans have been increasingly expanding into natural spaces to build homes, apartment complexes, shopping centres and more. In Massachusetts, for instance, “most of the roads that are being built nowadays are small subdivision roads,” Jackson says.

Aram J.K. Calhoun, professor emerita of wetland ecology at the University of Maine, says it’s “very common” to see development projects popping up near vernal pools in New England. Vernal pools are declining in parts of North America at an “alarming rate,” experts say, and human development is the most pressing threat to these bodies of water.

“Oftentimes developers don’t even know what they are,” Calhoun says. “Sometimes they get filled intentionally because they get in the way of a project, and sometimes they’re just overlooked.”

Imperfect solutions

Modifying curbs is a small part of the solution to maintain wildlife corridors in areas of human development, but Quinn says it goes beyond that. “Curbing is kind of a secondary thing when it comes to conservation. If a development gets approved in an area where there’s going to be migrating amphibians, the impact is already there regardless of whether there’s curbs.

“We need to be citing and permitting development in a much more effective way, one that is guided more by science and not by the monetary gain of a developer,” Quinn adds.

Endless roads have already been built, and most of them are here to stay. And with a lack of affordable housing becoming a growing problem in the U.S. and Canada, building houses – and the roads that come with them – is often cited as essential. For some of these roads, a means to mitigate the challenge to animals is both known and relatively inexpensive, a rare combination in wildlife conservation.

“You don’t need an expensive overpass; you don’t need a well-designed underpass. You just need to use a different type of curb,” Jackson says.

In the 1990s, Waterton Lakes National Park changed its vertical curbs into sloped curbs after a park employee noticed a lot of salamanders stuck on the road on a rainy night. Ottawa changed some of its curbs to help hatchling turtles in 2015, and in 2023, Trent University modified curbs to help salamanders after Hossie raised concerns. The Minneapolis parks department is currently replacing vertical curbs with sloped curbs on city properties.

Yet curb design is an imperfect solution. “Curb modification goes a long way to helping these animals, but it still doesn’t completely eliminate the threat of road mortality,” Hossie says. Animals still have to cross roads in the first place.

Tunnels and underpasses give animals an alternative to walking on roads, but they aren’t always effective. Some species are hesitant to use tunnels and for other species, scientists just don’t know yet how to create tunnels they’ll use. Tunnels also need fencing to lead animals into the structure. On smaller subdivision roads where traffic volume is projected to be low, curbs often make more sense than tunnels, Jackson says.

If vertical curbs are necessary, there are other options to relieve the pressure. Gaps can be cut into vertical curbs to give animals an exit. Alternatively, sloped curbs can be added only around catch basins. The rest of the road will have vertical curbing so there’s still a risk, but the number of animals falling into basins should decline.

To more fully combat the problem, some organizations are implementing multiple strategies. A few years after sloped curbs were installed at Waterton Lakes National Park, salamanders were still being hit by cars on high-traffic roads. Park staff had tunnels built under these roads. The Minneapolis parks department puts up turtle-crossing road signs during nesting and hatching season and has placed mesh material over catch basins to prevent animals from falling in.

Changing the way we design our curbs is never going to be a complete solution to reptile and amphibian road mortalities. The scale of the problem is simply too massive. But by making this one small change, we can make it a little less risky for amphibians and reptiles to navigate human-altered landscapes.