Many modern cares are designed so that the people using them are protected in a passenger cell or safety cage. This is a rigid 'box' which is more likely to survuve and impact. The front compartment of the car is the crumple zone, which squashes up in a crash. This absorbs a lot of the energy of the moving car. At the same time, the heavy engine is directed downwards so that it is not pushed into the passenger cell.
When a car crashes, its occupant may be thrown about. The car stops, but the people keep on moving. They are likely to be thrown forwards, colliding with the windscreen or steering wheel. Seat belts help to keep the passengers in their seat. The inertia reels come into…