Roadkill is a serious problem in the United States. Just in the U.S., wildlife causes more than a million automobile accidents per year. These accidents cost $8 billion in medical care and car repairs. Cars kill more than a million animals every day. For many species, it is the main cause of death. Even worse, major roads can split up animal populations. They also destroy their habitats. That makes it much harder for many animals to find food and a mate.

People are beginning to understand how dangerous this can be. Highway crossings for animals have become more common. There are many types of crossings. They depend on the species that need to cross. They also depend on the geographic features of the land. Some of the most common are bridges, overpasses and tunnels. The crossings reduce the number of crashes and save animals.

Wildlife Bridges

Wildlife bridges are usually covered in vegetation. The purpose is to make them look natural and encourage animals to use them. Often fences are placed on the side of the road to direct wildlife toward the crossing.

Wildlife crossings began in France in the 1950s but really took off in the Netherlands. More than 600 crossings have been built there. The Dutch built the world's longest animal crossing, the Natuurbrug Zanderij Crailoo. It is more than 0.8 kilometers (0.5 miles) long. Wildlife crossings can also be found in Australia, Canada and other parts of the world. In the United States, the idea took a little longer to catch on. Wildlife bridges and tunnels began here less than 20 years ago.

Decorated to Look like a Frog Village

One of the earliest U.S. crossings was in Davis, California. In 1995, the city built a 15-centimeter (six-inch) wide tunnel to let frogs pass under a road. One end was decorated to look like a frog village and named Toad Hollow. Despite this, the frogs did not use it.

The crossings in Banff National Park in Alberta, Canada, are more successful. Between 1996 and 2016, 42 crossings were built across the Trans-Canada Highway. In that time, 150,000 animals have used them. The number of accidents involving wildlife went down 80 percent.

Auto Accidents

In Queensland, Australia, koalas (Phascolarctos cinereus) have declined very quickly in the last few decades. Auto accidents were one of the main causes, according to a government report. Between 2010 and 2013, Queensland built about a half dozen wildlife crossings. They used several drainage tunnels under roadways. Ledges were added, so small animals wouldn't get wet. One ecologist was surprised at how quickly the koalas began using the tunnels.

In recent years, animal crossings have been built in the western United States. Since 2000, Arizona has constructed at least 20 crossings. Each one has fencing. In a part of Arizona where elk (Cervus canadensis) migrate, there was a 90 percent drop in wildlife accidents. In 2018, Washington officials were working on wildlife bridges across Interstate 90. They will let animals pass between the northern and southern Cascade Mountain regions. Deer began using one of the bridges even before it was finished.

Some types of wildlife crossings can be expensive to build. They save money in the long run. Ecologists and conservation experts are hoping state lawmakers will continue building wildlife crossings.