Just like we build crossings to enable us to pass natural obstacles, wildlife crossings allow animals to pass human-made barriers. They're useful not just because they protect wildlife from being hit by cars, but also because they connect habitats fragmented by human activity. Wildlife crossings are not new practice in habitat conservation, but so far there aren't nearly enough.
Europe and especially Netherlands is leading the way in terms of wildlife crossings. European countries including the Netherlands, Switzerland, Germany, and France have been using various crossing structures to reduce the conflict between wildlife and roads for several decades.
The crossings themselves fall into many categories, with two main groups: underpasses and overpasses, and both of them have proven to be effective in terms of animal aid and aesthetics, with some actually becoming touristic attractions.
They can also be quite varied in nature.
I for one think this is a great idea and I'd love to see it implemented in more areas - what do you think?