InTrans / Aug 14, 2014

Why did the chicken (deer, raccoon, frog, wolf, snake, bird, bear, etc.) cross the road?

Go! Magazine

Truck cross bridge with bear underneathposted on August 14, 2014

While we’re barreling through the countryside at 55 mph or more, most of us give little thought to the critters who live or move about near the roads we’re traveling on. But roads, although greatly beneficial to humans, can be huge problems for other creatures. We can see evidence of some of the problems—like roadkill—almost every day. Others are not so easily noticeable by a casual observer.

Habitat fragmentation

Residential, commercial, and agricultural development—building homes and businesses and farmland and the related roads and other infrastructure—destroys animal habitat. Development also “fragments” habitat, dividing land into patches of isolated environments. Habitat fragmentation is especially dangerous for animals, like frogs, that need multiple environments throughout their life cycle. Similarly, roads split habitats. Roads can create an obstacle that animals need to cross to reach the environment they need on the other side. A less obvious form of fragmentation is caused by culverts (tunnels or open drains that go under roads, allowing streams to flow). Building roads over streams can restrict the ability of fish, like salmon, to swim upstream to spawn. Small culverts can be easily clogged with debris. Culverts can sometimes cause water levels drop too low for fish to pass through, or create currents too fast for fish to navigate.

Runoff woes

Culverts, channels, and bridges create places for chemicals or harmful materials on the roadway to leak directly into ground water or bodies of water. Some of these chemicals can harm animals living in the water (namely fish, amphibians, and reptiles) as well as animals that drink the water. Runoff containing salt used to de-ice roads also harms roadside plants and gets into the water, damaging or killing flora near rivers.


The exact number of animals killed by vehicles every year is unknown, but estimates range in the millions. Big and little creatures venture across roads as they move from place to place to feed, mate, and lay eggs. Large herbivores (like deer or moose), omnivores (mostly bears), and predators (like snakes, bobcats, and skunks) have large ranges, making it almost inevitable that they will have to cross a road at some point.

An animal on the pavement can be just as fatal for humans. According to the Federal Highway Administration, every year more than 200 people are killed and thousands more are injured in collisions with large animals; the related cost of damages and medical expenses reaches almost $200 million.

For slower-moving animals, notably reptiles such as turtles, crossing roads is particularly dangerous as they cannot quickly react to cars. Many mammals have faster reaction times. But once they’ve set foot on the pavement, larger, slower beasts often cannot move out of the way of approaching vehicles fast enough. Several solutions have been implemented in the United States to reduce road kill. Often these projects are designed around endangered species, but they help any animals that cross roads. Many of these projects are not widely implemented, as different animals require different approaches to reduce roadkill.

Tortoise Underpass: California

Desert tortoises in California live up to 70 years and mature almost as slowly as they move. They have become endangered because they are highly vulnerable on roads. One solution in California is to build “tortoise underpasses” or culverts that tortoises use to pass safely under roads instead of on top of them.

Culvert upgrade: Washington

Many culverts are along fish migration routes to their breeding grounds. The Washington State Department of Transportation and Department of Fish and Wildlife are identifying problem culverts and redesigning and rebuilding them to improve conditions for migrating fish.

Bear underpass: Florida

Black bears have ranges from 11 to 66 square miles. The Florida Department of Transportation and Fish and Wildlife Conservation Commission have identified locations where black bears often cross roads and are killed or injured. Working together, the two agencies have created large underpasses that connect large swaths of bear habitat.

Amphibian/reptile walls: Florida

Three-and-a-half-foot walls with lips at the top (similar to walls in zoos) have been constructed along a 2-mile stretch of Florida road. The lip makes it difficult or impossible for animals to climb over. In addition to the walls, there is a system of culverts for animals to use to pass safely underneath the road.

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By Brandon Hallmark, Go! Staff Writer

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