When two cars are going 40mph there is an immense amount of kinetic energy. That kinetic energy has to go somewhere in order for those cars to stop. It can go into the frame of the car, it can go into the passengers, and it will into heat and noise. But it has to go somewhere. Until they build cars out of space Nerf they found on a passing comet we can choose to have the car crumble and absorb the impact or have the passengers absorb it.