Wildlife crossings with exclusion fencing
Underpasses, overpasses and rope or pole bridges, paired with fencing that funnels animals to them, reconnect habitat split by roads and stop roadkill.
Start small
Map the local roadkill hotspot: over 3 months, 3 to 5 volunteers log koala sightings and road deaths on one road stretch (free via iNaturalist or a council app), then take the data to the council or state road authority asking for koala fencing, signage and a retrofit of an existing culvert with a dry ledge and plantings at entrances (often a few thousand dollars per culvert, paid by the road authority). Add 2 to 4 motion cameras (about AUD 300 to 500 each) to monitor use.
The problem
Roads fragment native koala habitat and kill koalas on the move, isolating populations; crossings with fencing keep koalas off the road while letting them reach food trees, mates and dispersal habitat on the other side.
Where it fits
Proven where a road cuts through known habitat or movement paths and the road authority funds structures as part of an upgrade or retrofit (Banff, Trans-Canada Highway; NSW Pacific Highway upgrades). Needs mapping of crossing hotspots and roadkill data, structures sized and furnished for target species (for koalas: dry ledges or furniture, vegetation at entrances, nearby food trees), continuous exclusion fencing with koala-proof tops and escape points, long-term monitoring and a maintenance budget.
The principle underneath
Animals follow fences; continuous exclusion fencing removes the road as a mortality sink and funnels movement to safe passages, while the passages keep gene flow and access to resources across the barrier. Success scales with structure density, fence integrity and time for animals to learn the routes.
A pattern in nature
Riparian strips and interlocking tree canopies act as natural corridors that let animals cross open gaps between habitat patches without exposure.
Who to call
Transport for NSW (Pacific Highway koala management and monitoring); Queensland Department of Transport and Main Roads (fauna sensitive road design); Parks Canada Banff highway mitigation team; Ross Goldingay (Southern Cross University) and Darryl Jones (Griffith University), road ecology researchers; Sandpiper Ecological Surveys (W2B koala monitoring); local koala groups and wildlife carers.
Watch out for
Fence gaps at driveways, intersections and fence ends; tops koalas can climb; flood damage; underpasses built too long, wet or dark with no cover; predators (foxes, dogs) at entrances; monitoring that stops too soon to show use (some species take years to learn); building crossings without protecting habitat on both sides; no maintenance budget.
Where it comes from
Modern road ecology grew from European fauna passages and North American highway mitigation; Banff National Park on the Trans-Canada Highway (highway twinning from 1981, monitoring since 1996) became the global reference. Australian fauna-sensitive road design (Queensland and NSW) adapted it for koalas and arboreal species. Open engineering and ecological practice; no restricted knowledge. Where crossings sit on Aboriginal Country, involve Traditional Owners in planning.
Where it's worked
Oxley Highway (Port Macquarie) and Pacific Motorway (Glenugie), NSW, Australia · 2013 to 2016
Camera monitoring of 12 underpasses found heavy use by wallabies, bandicoots, echidnas and lace monitors and no consistent support for the 'prey trap' fear, but koala use was very low (about 3.4 passes per year at Port Macquarie, one detection at Grafton).
Peer reviewedSource
Woolgoolga to Ballina Pacific Highway upgrade, northern NSW, Australia · Koala monitoring Year 6, 2022 to 2023
Koala exclusion fencing (2 km of Wardell Road, 3 km of the old Pacific Highway) and three crossing structures: no koala vehicle strikes on those roads since fencing, against 10 in 2016/17; no koala road deaths in sections 1 to 11 in Year 6; Bagotville population stable (about 171 koalas against a 174 baseline).
DocumentedSource
Banff National Park, Alberta, Canada (Trans-Canada Highway) · Monitoring 1996 to 2012; highway twinning completed 2014
44 crossing structures (38 underpasses, 6 overpasses) plus 82 km of fencing cut wildlife-vehicle collisions by more than 80% (over 96% for elk and deer); wildlife used the crossings over 150,000 times, including grizzly bears, wolves and cougars.
DocumentedSource
Where it failed
Koalas used underpasses rarely in peer-reviewed camera monitoring on NSW highways: about 3.4 koala passes per year across three underpasses at Port Macquarie, two underpasses never used, and a single detection at Glenugie near Grafton over 2 to 3 years. On the Woolgoolga to Ballina Pacific Highway upgrade, koalas were killed where fencing lacked metal sheeting or a floppy top, flood and erosion destroyed about 250 m of fauna fence, and a breach at Laws Point went unnoticed until found on monitoring. Structures without continuous, maintained fencing largely fail.
Related Fruit
- SaplingVolunteer koala corridor planting on private landA community group links up farms and backyards with volunteer-planted koala food trees to reconnect fragmented habitat.
- TreeCommunity forest managementLegal rights to manage, use and earn from forests go to organised local communities, which then protect them better than many parks do.