The following three safety features work based on the same principal. They increase the time that the force is applied across. In order to see how this helps the passengers, you have to use the momentum definition of force.
$$ F = \frac{\Delta p}{t} $$
In this scenario, $\Delta p$ is constant. That means that in order to reduce the force that acts on the passenger, $t$ has to increase.
Seatbelts prevent you from moving around a lot during a collision. However they also are designed to stretch a little. This is because the stretching increases the time across which the force is applied on the body.
Airbags increase the time taken for the head’s momentum to reach 0. Airbags also prevent cuts.
Crumple zones are areas of a vehicle that are designed to crush in a controlled way in the event of a collision. They increase the time for the momentum of the car to reach 0.