Just a few points to help you along:
1) roads have got to be made of something which retains, as much as possible, friction when wet. Additionally, it can't break up often, which could lead to pots holes etc.
2) the rails on the sides of highways, small bushes near highways etc are all ways of slowing down a car without placing high amounts of stress on the occupants.
3) the front of the car has to be able to crumple to reduce the force, while the occupant cage has to be strong to ensure the safety of the occupants.