Eventually, better materials and robotic construction is going to be very cheap and roads will move under ground. Or these overpasses will be built. Or roboti

Eventually, better materials and robotic construction is going to be very cheap and roads will move under ground. Or these overpasses will be built. Or robotic vehicles will all slow down as animals approach a highway, while other smaller robots (maybe drones) herd them across with sound effects. One way or another, this problem will be solved. How all these technologies will evolve and which ones will solve it first is anybody's guess.