Wildlife overpasses have long been thought to help reduce wildlife roadkill, by providing them with a safer option for crossing roads. However, recent publications are showing that these structures can help with an even more pervasive problem over time - roads acting as a barrier to gene flow.
It has been shown that highways that host > 10 vehicles per hour can start to measurably deter grizzly bears, particularly females, from crossing busy roadways. Over time, this can lead to measurable genetic changes in populations on either side of the road. Eventually, it is projected that decreased breeding across a major roadway can lead to populations having insufficient genetic diversity to thrive.
A recent study conducted by researchers at Montana State University and published in the Proceedings of the Royal Society B showed that grizzly and black bears were able to utilize wildlife overpass structures to rendezvous with members of the opposite sex on either side of the Trans-Canada Highway in Banff National Park. In fact, one black bear male in the study became quite the stud with use of the overpass, mating with at least five different females and fathering at least 11 offspring while crossing back and forth over the road!