An idea proposed by an Australian park ranger more than five decades ago has finally become a wildlife crossing. In 1974, Royal National Park ranger Bob Crombie suggested using Cawleys Bridge to help animals safely move between areas of bushland separated by a major road. In 2026, the bridge was transformed into a dedicated wildlife corridor above the Princes Motorway in southern Sydney. According to the NSW Government’s Environment and Heritage department, the upgraded bridge reconnects habitat between Heathcote National Park, Garrawarra State Conservation Area and Royal National Park, creating a safer route for koalas, wombats, quolls and other native animals.
An idea from 1974
Cawleys Bridge was not originally built as a wildlife crossing. The structure was designed as a service bridge, providing access for utilities and road-management activities above the motorway. But shortly after the motorway was built, Crombie recognised that it was creating a significant barrier for wildlife. He proposed using the existing bridge to allow animals to move between habitats on either side of the road. The idea came at a time when wildlife connectivity was receiving far less attention in road and infrastructure planning than it does today. As a result, Crombie’s proposal remained unrealised for decades. The concept eventually gained renewed attention as concerns grew about habitat fragmentation and the dangers wildlife faced attempting to cross busy roads.
A dangerous divide
The Princes Motorway has become a major transport route through the region, carrying around 40,000 vehicles a day. For wildlife, the busy road represents a major physical and safety barrier. The motorway separates areas of habitat associated with Heathcote National Park, Garrawarra State Conservation Area and Royal National Park. Animals moving between these areas risk being struck by vehicles when attempting to cross the road. Hundreds of animals have been killed on roads in the wider area, highlighting the need for safer connections between fragmented habitats. The Cawleys Bridge project provides an opportunity to reconnect these landscapes without requiring animals to cross the motorway itself.
Turning a bridge into habitat
Instead of building an entirely new wildlife overpass, authorities chose to retrofit the existing Cawleys Bridge. The bridge is about 70 metres long and 7.5 metres wide. Part of the structure continues to be available for emergency and management access, while another section has been adapted specifically for wildlife.The transformation includes vegetation, soil, logs and other natural features intended to make the crossing resemble the surrounding environment. The design also recognises that different animals move in different ways. Ground-dwelling species can use vegetated areas, while ropes and elevated structures provide routes for animals that travel through trees or glide between them.
Koalas get a safer route
Koalas are among the species expected to benefit from the new connection. According to the NSW Government, the crossing can help link koala and wombat populations in Heathcote National Park with habitat extending toward Garrawarra State Conservation Area and Royal National Park. Maintaining connections between habitat areas is important because fragmentation can isolate animal populations. A connected landscape allows wildlife to move in search of food, mates and suitable shelter and can provide alternative areas when local conditions change. For koalas, which depend heavily on suitable forest habitat, maintaining these connections can be particularly valuable.
Designed for many species
The crossing is not intended only for large or well-known animals. Features have been incorporated for a variety of species, including wombats, quolls, gliders, possums, reptiles, amphibians and smaller ground-dwelling animals. Vegetation provides cover and food opportunities for some species, while logs and other structures create shelter. Ropes offer an alternative pathway for animals that normally move through the tree canopy.This multi-species approach is important because an effective wildlife crossing needs to accommodate different movement behaviours rather than simply providing a large open bridge.
Tracking wildlife use
Building the crossing is only part of the project. Researchers and authorities also need to determine whether animals actually use it. Monitoring has been incorporated to observe wildlife movements and understand how different species respond to the new habitat connection. Cameras, infrared technology and acoustic monitoring can help identify animals using the crossing, including species that may be difficult to observe directly.Such monitoring can show whether animals are avoiding the motorway and adopting the safer route, as well as which features of the crossing they prefer. The information could also help inform the design of future wildlife crossings elsewhere.
A 52-year-old idea comes alive
The Cawleys Bridge project represents an unusual example of an old infrastructure idea being adapted for modern conservation needs. What began in 1974 as Bob Crombie’s proposal to turn a service bridge into a wildlife corridor has taken more than five decades to become reality. The finished crossing now sits above a motorway used by tens of thousands of vehicles every day, providing animals with an alternative to navigating one of the region’s most dangerous barriers. Rather than allowing a road to permanently divide two areas of habitat, the project has turned an existing bridge into a connection between them. For wildlife moving through southern Sydney, Cawleys Bridge is no longer simply a piece of transport infrastructure. It is now intended to function as a pathway through a fragmented landscape, reconnecting habitats that animals have struggled to reach safely for decades.
