The sides of the car do not have crumple zones, which means we are much more vulnerable in side-on collisions.
The first line of protection in a collision is the car's protective body. The front and rear parts of the car consist of so-called crumple zones that are developed to collapse during a collision, so that the sequence of events is slowed down.
In a frontal collision, the car's front crumple zone is compressed to absorb the energy from the impact within the outer parts of the vehicle, rather than being directly transferred to the occupants of the car. In a rear-end collision the car's rear crumple zone is compressed.