A wildlife crossing is a bridge, tunnel or culvert built so animals can cross a road without stepping onto it. From the green overpasses of Banff to the record-breaking crossing taking shape over the 101 Freeway near Los Angeles, these structures have become one of the most effective ways to cut collisions and reconnect habitat split by highways.

Vegetation-covered wildlife crossing spanning a highway through forest
A vegetation-covered wildlife crossing spanning a highway through forest. Image via Valhalla.

Why roads need wildlife crossings

Animals move to feed, breed and find new territory. A busy highway cuts across those routes, killing animals, endangering drivers and splitting populations into smaller, isolated groups. Fencing alone keeps animals off the tarmac but leaves them stranded on one side. Crossings combined with fencing solve both problems: the fence funnels animals towards a safe route over or under the road.

The idea is not new. The first overland wildlife crossings were built in France in the 1950s. Today they are part of road planning from the Netherlands to the Canadian Rockies.

Types of wildlife crossing

Different animals need different designs:

  • Overpasses, also called green bridges or ecoducts, carry soil, shrubs and trees across the road and suit large animals such as deer, elk and bears.
  • Underpasses and viaducts let animals pass beneath the roadway, often along a stream or valley floor.
  • Culverts and small tunnels serve otters, badgers, hedgehogs, amphibians and reptiles.
  • Canopy bridges are rope or mesh crossings for tree-dwelling animals such as monkeys and squirrels.
A broad green wildlife overpass above a divided roadway
A broad green wildlife overpass above a divided roadway. Image via Earth Porn.

Banff: the world's longest-running crossing study

Banff National Park in the Canadian Rockies is the classic example. Work to widen 82 kilometres of the Trans-Canada Highway from two lanes to a four-lane divided highway began in 1981 and was completed in January 2014. Along the way, Parks Canada built 6 overpasses and 38 underpasses, linked by 82 kilometres of fencing.

The results are striking. Wildlife-vehicle collisions fell by more than 80 percent, and by more than 96 percent for elk and deer. Between 1996 and 2012, animals used the crossings more than 150,000 times. Eleven species of large mammal have been recorded, including grizzly and black bears, wolves, cougars, moose, elk, bighorn sheep, wolverines and lynx. Monitoring has run since 1996, making it the longest-running wildlife crossing research programme in the world.

Wildlife crossings in the United States and Europe

In the United States, crossings are now part of major highway projects:

  • Interstate 90, Snoqualmie Pass, Washington: a wildlife overcrossing was built as part of a 15-mile safety project between 2015 and late 2019.
  • Interstate 80, Parleys Canyon, Utah: an overpass about 110 metres long and 15 metres wide, completed in early 2019.
  • Interstate 75, Florida: 24 underpasses and 12 modified bridges along 40 miles in Collier and Lee counties protect the endangered Florida panther.
  • Wallis Annenberg Wildlife Crossing, Agoura Hills, California: billed as the largest wildlife crossing in the world, it spans 10 lanes of the 101 Freeway and Agoura Road to reconnect habitat for mountain lions and other wildlife in the Santa Monica Mountains. Construction began on Earth Day 2022 at a cost of $114 million, with a ribbon-cutting planned for 2 December 2026.

In Europe, the Netherlands has more than 66 overpasses and ecoducts, built mainly for badgers, wild boar and deer. Its Natuurbrug Zanderij Crailoo, completed in 2006, is about 800 metres long and 50 metres wide, and is often described as the world's longest ecoduct.

Are wildlife crossings worth the cost?

One study estimated that adding crossings raises the total cost of a road project by about 7 to 8 percent. A Virginia Department of Transportation study found that a deer underpass pays for itself in avoided property damage once it prevents roughly 2.6 to 9.2 deer-vehicle collisions a year, depending on its cost. Add the human injuries avoided and the benefit to wildlife populations, and the case becomes strong.

Crossings are built for animals, so admire them from viewpoints and never stop on a highway to look for wildlife. For other ideas about sharing routes with animals, read Duck Lanes on London Canal Towpaths: The Share the Space Campaign and Turtle Tunnels on Japan's Railways: JR West and the Suma Aquarium.

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