Designing crossing structures for wildlife underneath roads is a challenge because species may respond differently to factors such as nearby habitat or crossing-structure dimensions. Here we show that large, open crossing structures along natural travel corridors accommodate the highest diversity of large and medium-sized mammals.

Underpasses are a useful tool to enable wildlife to move across landscapes with roads. Not all ground-dwelling species of wildlife will find underpasses to their liking, but many do. Underpasses are also not a panacea for impacts on wildlife. And we shouldn’t use their effectiveness as a justification to run highways through pristine areas. They’re a tool to minimise impacts of road projects that have wide community support.

Route 34: Section Hacienda Barú Refuge is the first site in Costa Rica to have underpasses specifically for wildlife. After monitoring these structures, 21 vertebrate species have been recorded using them, preferring square, big underpasses with a natural substrate and vegetation cover.

Lighting in wildlife underpasses significantly reduces their use by bats. Bats are more likely to cross the road rather than use the underpasses when they are lit, greatly increasing their risk of mortality.

Many populations of amphibians are declining rapidly across Asia and road kill is a significant cause. In this project, we designed and tested a range of culverts to identify amphibian-friendly options to mitigate roadkill and barrier effects of roads.

Jaguars together with other neotropical species only used purpose-built wildlife underpasses under a highway in Mexico, even when ‘large enough’ drainage structures were available. Drainage structures may work as crossings for some species but can’t substitute proper wildlife underpasses.