Why do animals cross the highway? 
Do highway fencing and wildlife crossing structures work and do they reduce wildlife-vehicle collisions? 
Do animals prefer underpasses or overpasses? 
Is use of the crossing structures by wildlife changing over time? 
Does human use of a wildlife crossing affect how animals use them? 
How do small animals get across the highway? 
What is the greatest threat to healthy wildlife populations? 
How do we know where to put future wildlife crossings? 
Why are animals still occasionally killed on the highway? 

Principles of Road Ecology
10 Quick Facts about Wildlife Crossing Structures  


Why do animals cross the highway?

Animals need to cross the highway to search out companionship, mates, food, shelter, and in some cases, to escape predators.

Do highway fencing and wildlife crossing structures work and do they reduce wildlife-vehicle collisions?

It took up to five years for some wary species, like grizzly bears, to start using wildlife crossing structures; however, most species are now using them to safely cross the Trans-Canada Highway (TCH). Since fencing and crossing structures were first constructed, wildlife-vehicle collisions have dropped by more than 80%.

Do animals prefer underpasses or overpasses?

Wildlife use underpasses and overpasses alike; however, when given a choice each species seems to have distinct preferences. Grizzly bears, wolves, elk, moose and deer prefer crossing structures that are high, wide and short in length, while black bears and cougars tend to prefer long, low and narrow underpasses.

Is use of the crossing structures by wildlife changing over time?

Yes. As wildlife populations fluctuate, the number of occasions individuals of a particular species use the crossings also rises or falls. We have also learned that some animals need time to adapt to new structures on the landscape. For example, overpass use gradually increased for grizzly bears, cougars, and wolves over the first five years of monitoring.

Does human use of wildlife crossings affect how animals use them?

Yes. When people use crossings, animals tend to use them less. Human use of overpasses is prohibited in Banff National Park.

How do small animals get across the highway?

Small and medium-sized animals, such as snowshoe hare, pine marten, fisher, porcupine, squirrels and voles, have different requirements for movement across the TCH. Pine martens, snowshoe hare and red squirrels used drainage culverts more often when traffic volumes were high, while coyotes used them less.

What is the greatest threat to healthy wildlife populations?

Road-kill has an immediate and direct effect on a population, easily seen within one or two animal generations. On the other hand, complete barrier effects (i.e. not being able to cross an obstacle like a highway) can take several generations to develop within a population. Barrier effects on a grizzly bear population may take as long as 50 years to measure and can have serious repercussions on genetic diversity and overall health.

How do we know where to put future wildlife crossings?

Over the years, information about where different species are most likely to cross the highway has been collected using:

  • radio telemetry monitoring 
  • animal tracks in the snow 
  • wildlife observations, and 
  • road kill hot spots

Wildlife movement models were built using mapping software to predict the most likely locations for wildlife travel across the TCH based on topography and habitat data for five species (black and grizzly bears, wolves, elk and moose). Locations for future wildlife crossing structures were then identified.

Why are animals still occasionally killed on the highway?

Occasionally, individual animals do get into the highway right-of-way. Research is currently underway to test the use of “electro-mats” as an additional deterrent to wildlife at certain breaks in highway fencing. An electro-mat will provide a mild ‘sting’ to the paw, hoof or nose that touches it. While the shock does not harm the animal, it will hopefully encourage it to choose another path away from the highway.