Can't you check the distances between the cars on the road? Then when it finds a car infront of it, it will slow down and stop behind it. You could check which way point each car is heading for, then check if a car is on the same path.
This could also work for you. If you run out in the road, the car will screech it's brakes to try and avoid hitting you (it could swerv and do more damage, so it's not just your life that's in danger). A simple rotate to the left or right will do, no fancy physics. Then reset the simulation and leave a message telling you what you did wrong.
bleep bleep