Local conservation groups have praised the design of the new tunnels, saying the company and the Roads and Traffic Authority had been co-operative in seeking their advice. The Australia Koala Foundation estimates there are about 100,000 koalas scattered across the country, down from 10 million in the 1920s.

In NSW there are between 10,000 and 15,000 koalas, but it is believed about 4000 are killed each year by cars, dogs and habitat loss. These deaths had prompted animal protection groups to make a series of recommendations, including special koala tunnels under main roads. Wildlife surveys suggest that Port Stephens has the largest southerly population of koalas in the state, with estimates ranging from a few hundred koalas to about 1000.

President of the local Native Animal Trust Fund, Audrey Koosmen, said the company had "done a hell of a lot of work" trying to protect the koalas from the traffic. Mrs Koosmen said there were as many as 150 koala road deaths each year in the local council area. "The tunnels are some of the best constructions for animals I've seen," she said.

As part of the 10-year upgrading of the main route between Sydney and Brisbane, jointly funded by the NSW and Commonwealth governments, Thiess is building the 10 kilometre Karuah bypass at the western end of Port Stephens, through one of the most ecologically sensitive parts of the North Coast. The area includes wetlands, a state forest, a national park and Aboriginal heritage sites. A company spokesman said it had set out to reduce the wildlife road toll. Tunnels are already successful in other parts of the state. Species such as native rats, wombats, wallabies and the endangered tiger quoll use three tunnels under the F3 Freeway between Sydney and Newcastle. Koalas are also using underpass tunnels at Taree, Brunswick Heads and other spots along the Pacific Highway.

A plastic tube has even been strung above the busy Wakehurst Parkway in Sydney to allow possums and native rodents to cross safely. The Thiess spokesman said the firm built about 15 kilometres of "floppy" fencing alongside the new section of road to stop the koalas from climbing onto the highway.

"The animals find they can't climb over so they follow the fence line until they come to one of our fauna tunnels - and away they go."