It's a solution, but it relies on animals thinking like us and taking underpasses, overpasses etc, which is not quite possible. And besides, if the track is fenced for several kilometres, eventually some of the larger animals would just try to get over it and get stuck on the tracks, or just push it out of the way on to the tracks. For existing forest routes, we can try fencing nd patrolling, but in future at least some new practice has to come up. As it is , vast areas of forests have vanished till now. And now, we are again trying to put railway tracks and highways through the remaining tiny areas of forest that have been left free of human interference so far.