Aissa,

The mean force applied on the car is a function of the distance over which the car comes to a halt.

The kinetic energy of the car before impact equals the work done by crumpling the car.

KE = W

And as work = force x distance,

F = KE/d

So if the car is rigid and barely crumples, d is small and the impact force is high.

If the car is 'softer' and crumples over a larger distance the impact force can be lower.