The TransCanada Highway cuts across Banff National Park in Alberta, Canada, fragmenting critical habitat and creating a large barrier to movement for wildlife.
To facilitate individual movement, especially of large, wide-ranging species such as grizzly bears, wolverines, and elk, man-made overpasses and underpasses were constructed to span the highway and funnel individuals from one side to the other.
While some species take a long time to begin using these structures, they ultimately provide a critical connection between fragmented forests and allow for continued gene flow between populations. In addition, road closures and the removal of man-made structures have allowed natural corridors to re-emerge within the region.
The Netherlands contains over 600 man-made corridors, including overpasses and underpasses along busy highways. The longest of these, the Natuurbrug Zanderij Crailo, is an overpass that is 50m wide and over 800m long. It was completed in 2006, and spans a railway line, business park, river, roadway, and sports complex.
This corridor is part of larger protected area within the country, the Veluwe, which consists of 1,000 square kilometers of forest and other natural habitats. Species known to use these corridors include roe deer, red deer, wild boar, and the endangered European badger.
The U.S. Highway 93 North reconstruction project represents the most extensive wildlife-sensitive highway design effort in the United States to date. This project is within northwest Montana on the Flathead Indian Reservation, the homeland of the Confederated Salish and Kootenai Tribes.
To mitigate the expansion of this 56-mile long road section on the ecological and cultural integrity of the Reservation, the Montana Department of Transportation built 41 fish and wildlife crossing structures, 16 miles of wildlife fencing, 39 jump-outs, and many wildlife crossing guards. Camera traps have identified a variety of species using the crossing structures, including black bears, coyotes, bobcats, mountain lions, mule deer, and American badgers.
The annual migration route of millions of crabs on Christmas Island crosses roads, golf courses, and beaches. To help facilitate the mass migration, more than 20 kilometers of barriers were put in place to direct the crabs away from roads and into 31 crab underpasses. There is also a 5m-high crab bridge crossing at one of the area’s busiest roads.
Africa’s first dedicated elephant underpass connects Ngare Ndare Forest/Lewa with the Mt. Kenya Forest in central Kenya. The underpass was opened in 2010 and formerly re-establishes the only remaining connection between Kenya’s second largest elephant population in Samburu with the individiuals in Mt. Kenya.
Road underpasses specifically designed for elephants can also be found in China’s Mengyeng Nature Reserve and South Africa’s Addo Elephant National Park, and are planned in India’s Hosur-Krishnagiri section.
The Eco-Link@BKE is a 62m long ecological bridge that spans the Bukit Timah Expressway (BKE) in Singapore. It reconnects the Bukit Timah Nature Reserve and Central Catchment Nature Reserve, which were separated when the expressway was built in 1986. It is the only crossing of its kind in Southeast Asia.
More than 15 species of mammals and birds have been seen to use the corridor, including the common palm civet and the critically endangered Sunda pangolin.