Thats a very interesting thought. I've actually seen that come up many times in animal behavior discussions. The consensus seems to be that cars are still too new in the evolutionary history of animals. I'll buy that argument, but it still seems hard to completely understand. Hunters walking up on a deer are close to natural predators. Therefore, they can quickly adapt and change behavioral pattern due to increasedhunting pressure. Actually, I guess hunters could be considered natural predators now; it's been going on for a long time. The argument I've heard is that in the evolutionary history of most mammals, there has never been a predator such as a motor vehicle. Maybe we are currently witnessing natural selection inaction.

That would be a neat study. Not sure it would be possible with the ever increasing traffic volume.