Each year, U.S. drivers collide with 1 to 2 million large animals, often killing them and endangering the drivers.

Add in smaller creatures, and studies estimate up to 300 million animals die on U.S. roads annually. An astounding number.

This is because wildlife must roam, and always has -- to find food and water, breed and raise young, and migrate seasonally.

They often follow ecological corridors dictated by geography and natural resources.

These pathways could be millennia old. But in the last century, they’ve been dissected by roads and highways.

The result is that either animal populations become isolated in small areas, where they can starve, become prone to disease or inbreeding.

Or they cross roads and court danger.

This has led communities around the world to build thousands of wildlife crossings – bridges or tunnels that guide animals safely across roads, railways, and open development.

They’re usually constructed along existing animal corridors.

While often made of concrete, they’re covered in soil, plants, and rocks to simulate natural habitat.

They can be hundreds of feet long and cost millions of dollars. But their results are astonishing.

They’ve reduced animal mortality in problem areas by more than 90%, and saved drivers from thousands of accidents.

As human development continues to expand, wildlife crossings stitch ecological pathways back together.