One of the leading causes of wildlife fatalities are collisions with vehicles. It turns out that many species will use river and stream culverts as a means of safe passage under roads. Installing intentional animal passages or corridors can dramatically decrease the amount of human-caused wildlife fatalities.
In some places, including Canada, there are wildlife bridges under and over roads and highways. These "crossings" are constructed solely for the safe passage of animals; and there are studies to prove that it is working...Bannff National park in Canada has a great series of videos featuring trail cameras that were installed on these wildlife bridges. You can check out their efforts here: Banff National Park:Wildlife Crossings