Roads built by humans often divide animal habitats; animals must cross the road and dodge traffic to get to the land & resources on the other side - this leads to millions of animal deaths each year.
Underpasses have been constructed which allow animals a "subway" under the road. For example, a pilot project, carried out by the Florida Dept. of Transportation, built underpasses for black bears. Their research shows that all sorts of animals were photographed using the safe-passage under the road. This is a simple thing that we can do to help animals traverse our roads safely; animal underpasses can successfully reduce numbers of "road-kill." Underpasses are just one of a great many new kinds of structures and devices that help animals get across our roads! Nowadays, you may hear these structures referred to as "Green Bridges."