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.

The tiny Leadbeater’s possum is critically endangered from a combination of habitat destruction, timber harvesting, the effects of high-intensity forest fires, and habitat fragmentation from roads and fire-breaks. We tested two different designs of canopy bridges across roads in their forest habitat and both were used, reducing the risk of predation by terrestrial predators and wildlife-vehicle collision.

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.

We used custom-built cameras and image recognition software to evaluate the use and effectiveness of a tunnel and fence system for amphibians at a road mitigation site in England. Over four years, we found high rates of use of the tunnels, no roadkill, colonisation of newly-built ponds and a substantial increase in the population size of several species, including the nationally protected Great Crested Newt.

Water culverts along Autoroute 10 in Quebec are used considerably less than one would expect for designated wildlife passages for mammals, since out of 20 species present in the vicinity of the culverts, only about half of them were ever detected making a full crossing, and only two species highly tolerant to water crossed the structures on a regular basis (common raccoons and American mink). Water level and use of polyethylene as construction material were the strongest deterrents.

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.

The Hazel Dormouse is an arboreal mammal in Europe that are reluctant to cross at ground level. This study examines a bridge crossing structure, which shows its effectiveness for dormice in the UK.