It's Australia's first long-term study of underpasses, which explored the structures in Port Macquarie and Grafton over two years.

The researchers studied 12 road underpasses including five under the Oxley Highway at Port Macquarie; and seven under the Pacific Highway south of Grafton.

Wildlife detection cameras were used to show more than 4800 mammals and goannas utilising the underpasses.

Species including eastern grey kangaroos, swamp wallabies, red-necked wallabies, red-necked pademelons and lace monitors crossed some underpasses more than once per week.

Rufous bettongs and echidnas crossed individual underpasses every two to four weeks.

Southern Cross University lead researcher Ross Goldingay said the crossing rates suggest animals used the underpasses to forage on both side of the freeways.

Ultimately the research findings show underpasses can lessen the impact of highway upgrades on Australia's native wildlife populations.

"This research provides compelling evidence that highway upgrades in Australia need not threaten wildlife populations if road underpasses are installed," Associate Professor Goldingay said.

"The underpasses are installed in conjunction with mesh fences (often with a floppy top to stop koalas climbing over) that line the highways to keep animals off the road and direct them to the underpasses to cross."

However, Associate Professor Goldingay said future road network expansions should not be justified by the findings.

"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.

"Underpasses are a useful generic tool to enable wildlife to move across landscapes with roads. But not all ground-dwelling species of wildlife will find underpasses to their liking but so far many do."

The predators detected at the underpasses were the introduced red fox (pest), feral cat (pest) and dingo.

"We did not see increased activity at the underpasses, allaying concerns of the 'prey-trap hypothesis' - whereby predators might easily pick off unsuspecting animals funnelled into the confined space of an underpass," Associate Professor Goldingay said.

"Only the fox was detected frequently enough to be a potential concern. However, its activity coincided less than expected with the activity of the mammals most at risk to it. In fact, potential prey may actually avoid using the underpasses when foxes are about."