Animal crossing: structures designed to save animals also improve road safety

Roads and cars are responsible for killing hundreds of millions of creatures every year. But two recent studies, including one from New South Wales, show animal crossings over or under highways are highly effective.

They not only save animals but potentially humans too.

A long-term study by Southern Cross University of road underpasses in the 240 km stretch of highway between Grafton and Port Macquarie, north of Sydney, found thousands of animals used the crossings in a two-year period.

The study is published in Ecology and Evolution.

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Wildlife cameras monitored the use of 12 highway underpasses over two years.

More than 4,800 medium to large animals were caught on camera using the crossings. It’s a number lead researcher Associate Professor Ross Goldingay describes as “quite astounding”.

The cameras detected eastern grey kangaroos, swamp wallabies, red-necked wallabies, red-necked pademelons and lace monitors crossing more than once a week. Rufous bettongs and echidnas were clocked crossing at individual underpasses every two to four weeks.

Goldingay says the results provide “compelling evidence that highway upgrades in Australia need not threaten wildlife populations if road underpasses are installed”. However he cautions this should not be used to justify unnecessary road expansion.

“Australia’s wildlife species are increasingly threatened with extinction by habitat clearing and fragmentation. One leading cause of this is the expansion of our road network, particularly the upgrade and duplication of major highways,” he says.

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Read more: How did the koala cross the road?

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The study also helps allay fears that predators like foxes, feral cats and dingos use these crossings like traps, taking advantage of the way tunnels funnel unsuspecting animals into a confined space.

Only foxes were detected hanging around underpasses more frequently than they were found in the surrounding forest. Yet fox activity rarely coincided with times when smaller animals (potential prey) were using the crossings.

An estimated 10 million animals die on Australian roads each year.  In the United States more than 350 million animals are killed by traffic, and in Europe, surveys suggest the annual toll is 194 million birds and 29 million animals. Amphibians and reptiles are also vulnerable, but not studied to the same extent.

A study by Washington State University in the US found animal crossings reduced vehicle collisions with wildlife for up to a ten-mile radius around 13 wildlife bridges and underpasses.

“Wildlife crossing structures not only benefit the ecosystem but may also improve road safety,” says Wisnu Sugiarto, author of the study published by the Transportation Research Board.

Wildlife structures can range in cost from US$500,000 for a tunnel-like underpass to over US$6 million for a broad bridge.

Deer, the animals most likely to be involved in vehicle collisions, were more likely to use bridge crossings, while underpasses appeared to be more popular with predators like black bears.

During the study time-period, there were more than 1,600 wildlife-vehicle crashes every year in the state with about 10% resulting in human injury and even a few deaths.

“Decreasing these accidents would reduce unnecessary trauma and potentially save lives in addition to saving money,” Sugiarto says.

The finding that wildlife crossings improve road safety aligned with the results of similar studies in other US states.