The survival of many species in particular areas depends on their ability to move across the territory. When a road cuts through a place, animals like squirrels, snakes, insects, etc are put into immense danger. In the article I read, it talked about how many snake species in the western ghats in India are being threatened because they get killed regularly by vehicles while crossing roads. Poor things can't even be seen by the incoming cars and trucks, and you can't really blame them for being so short that they can't see the fast incoming vehicles in time to dodge them.
Maybe making small drains / tunnels below the roads at various points could help. Just a simple pipe that's put across the road, before laying it on. And the ground around those places could be leveled in such a way as to channel the critters to the pipes. Such channels below the road are probably used at places for handling rainwater flowing downhill. But we probably need to enlarge them to accommodate the animals as well.