Every single day, over one million animals are run over and killed by cars on US roadways. These animals are just trying to get from one side of the road to the other, an increasing challenge with the constant addition of new roads.
Some highways have found ways to keep wildlife from crossing the road, while this might decrease road kill it presents another issue. Many factors threaten a population when they are isolated to a particular area, such as lack of genetic diversity. Also the risk for disease and famine increases. In other words, if any specie wants to survive it will eventually have to find a way to the other side.