You could have tiles forget the scent/roads forget the traffic. With each simulation step, decrease it until it's gone after however long you want it to be reme

You could have tiles forget the scent/roads forget the traffic. With each simulation step, decrease it until it's gone after however long you want it to be remembered. Then, ghosts would have to be somewhat near pacman, and cars are only influenced by what goes on around them, not what happened a while ago. Of course, simulating the actual view of a driver, i.e., excluding things behind the vehicle etc., takes a lot more work.