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Of course growing up you heard the joke “Why did the chicken cross the road?” and  The answer : “To get to the other side.” Well now, we know the truth, it was because there wasn’t an underpass.

"Why did the chicken cross the road?"  because there wasn't an underpass.

“Why did the chicken cross the road?” because there wasn’t an underpass.

Joking aside, where you ever in the position of driving and suddenly had to stop because of an animal in the road? Sometimes people laugh out of nervousness, children get excited about seeing the “cute animals cross”, or they become angry. Angry because of the sudden feeling of being unsafe or as I once heard someone say, “do they really have to pass here”, as if their territory was invaded. Today we will discuss the captivating structures of wildlife crossings; we will define what are wildlife crossings, why wildlife and humans meet on the roadways, state the benefits of animal crossings, and give a few examples.



“Wildlife crossings are structures that allow animals to cross human-made barriers safely. Wildlife crossings may include: underpass tunnels, viaducts, and overpasses (mainly for large or herd-type animals); amphibian tunnels; fish ladders; tunnels and culverts (for small mammals such as otters, hedgehogs, and badgers); green roofs (for butterflies and birds).[¹]   

Image Source: THE WORLD GEOGRAPHY Ecoduct The Borkeld, Netherlands

Example 1
Ecoduct The Borkeld, Netherlands.

Another term you may hear is “Wildlife corridor”

Wildlife corridors are remnant habitat, regenerated habitat or artificially created habitat that links larger areas of wildlife habitat.  Corridors provide a means by which animals and plant seeds can move between larger areas of habitat that are their refuges, within an otherwise uninhabitable environment.[²]

Wildlife movement corridors, also called dispersal corridors or landscape linkages as opposed to linear habitats, are linear features whose primary wildlife function is to connect at least two significant habitat areas (Beier and Loe 1992).[³]

According to Senior Environmental Planner Barbara Marquez, “Without linkages, wildlife populations are in danger of inbreeding, starving, becoming aggressive toward humans and, ultimately, extinction,” she said.[4]

Example 3  Image Source: THE WORLD GEOGRAPHY  Ecoduct The Borkeld, Netherlands

Example 2
“Animal bridge” in Montana, USA

Why wildlife and humans meet on the roadways:

In order to build passage ways, buildings for humans, increase agriculture, receive electricity, install pipelines, we dig deeper and deeper into the lands where animals once roamed in search of food, water, mate, shelter. The term for this displacement or separation is “Habitat and population fragmentation.”

“Population fragmentation occurs when groups of animals living in the wild become separated from other groups of the same species. Population fragmentation is often caused by habitat fragmentation, which as the name implies describes the emergence of discontinuous habitat (fragmentation) in the environment. Habitat and population fragmentation can be caused by natural processes or by human activity such as land conversion. The extent to which habitat fragmentation leads to population fragmentation, however, differs among landscapes and taxa. The pattern of subdivision in Cross River gorilla populations has been found to correspond largely to recent patterns of habitat fragmentation caused by anthropogenic activities (Bergl & Vigilant, 2006).”[5]

For example the picture below shows a road cutting through the land causing a fragmentation(divide) in wildlife “habitat”.

Image Source: Izismile Banff National Park, Alberta, Canada

Example 3
Image Source: Izismile
Banff National Park, Alberta, Canada.

Effects of  Habitat fragmentation:

Habitat fragmentation affects numerous ecological process across multiple spatial and temporal scales, including changes in abiotic regimes, shifts in habitat use, altered population dynamics, and changes in species compositions (Schweiger et al. 2000).[³]

Jaeger et al. (2005) identify four ways that roads and traffic detrimentally impact wildlife populations: (1) they decrease habitat amount and quality, (2) they increase mortality due to wildlife-vehicle collisions (road kill), (3) they prevent access to resources on the other side of the road, and (4) they subdivide wildlife populations into smaller and more vulnerable sub-populations (fragmentation). Habitat fragmentation can lead to extinction or extirpation if a population’s gene pool is restricted enough.[¹]

Loss of human life. Bruinderink & Hazebroek (1996) estimated the number of collisions with ungulates in traffic in Europe at 507,000 per year, resulting in 300 people killed, 30,000 injured, and property damage exceeding $1 billion.[¹]


Example 4
Wildlife overpass near Keechelus Lake, Washington, USA

Benefits of animal crossings:

Animal crossings maintain biodiversity, lower incidence of disease, allow populations to interbreed, increase genetic diversity, provides access to larger habitats,and basic needs such as food and shelter.  Moreover, animal crossings provide a safe movement for both humans and animals.

Benefits of animal crossings:The statistics

A joint Miistakis Institute and Western Transportation Institute (WTI) study demonstrates the wildlife underpass in Dead Man’s Flats is improving human safety by reducing the number of wildlife-vehicle collisions in the area

The underpass southeast of Canmore has proven more cost effective than the societal costs paid for damaged vehicles, human injury and death, and lost hunting revenues.

An analysis of the underpass, which includes three kilometres of fencing along a section of the Trans-Canada Highway, demonstrates a significant reduction in the total number of wildlife-vehicle collisions per year, from 12 to three accidents per year, since the underpass was installed in 2004.

The Highway Wildlife Mitigation Opportunities for the Trans-Canada Highway in the Bow Valley report clearly demonstrates the cost effectiveness of the wildlife underpass, having reduced the average annual societal cost by over 90 per cent – from $129,000 to $18,000 per year.”[6]

Example 5 Image Source: cbc news Grizzly bear emerging from an underpass after crossing the Trans-Canada Highway in Banff National Park.

Example 5
Image Source: cbc news
Grizzly bear emerging from an underpass after crossing the Trans-Canada Highway in Banff National Park.


The conservation issues associated with roads (wildlife mortality and habitat fragmentation) coupled with the substantial human and economic costs resulting from wildlife-vehicle collisions have caused scientists, engineers, and transportation authorities to consider a number of mitigation tools for reducing the conflict between roads and wildlife. Of the currently available options, structures known as wildlife crossings have been the most successful at reducing both habitat fragmentation and wildlife-vehicle collisions caused by roads (Knapp et al. 2004, Clevenger, 2006).[¹]

Example 6 Image Source: THE WORLD GEOGRAPHY Wildlife crossing over Compton Rd (SR30) at Kuraby near Karawatha Forest, Queensland, Australia

Example 6
Wildlife crossing over Compton Rd (SR30) at Kuraby near Karawatha Forest, Queensland, Australia


[¹]World Heritage Encyclopedia. (n.d.). Wildlife crossing | World Heritage Encyclopedia. Retrieved from http://cdn.worldheritage.org/articles/Wildlife_crossing#cite_note-1

[²]Wildlife Corridor. (n.d.). Retrieved from http://www.greenway.org.au/biodiversity/g-wildlife-corridor

[³]Bond, M. (2003, October). Principles of Wildlife Corridor Design. Retrieved from http://www.biologicaldiveristy.org/publications/papers/wild-corridors.pdf

[4]Gish, J. (n.d.). Inside Seven – Caltrans, District 7 – Monthly Newsletter. Retrieved from http://www.dot.ca.gov/dist07/Publications/Inside7/story.php?id=558

[5]A.P.E.S. (n.d.). Retrieved from http://apesportal.eva.mpg.de/status/topic/status/population_fragmentation

[6] Wallace, J. (2012, November 5). Underpassing grade | News & Events | University of Calgary. Retrieved from http://www.ucalgary.ca/news/utoday/november5-2012/overpass