A few days ago a policeman held a speach at our school about driving carefully, not drinking and driving, and things like that. One interesting thing he showed us was a way to "simulate" a slow car crash.
Let's imagine you are driving at 7 km/h - which is in fact an unlikely low speed for driving - and you suddenly stop in a dead halt. The effect on your body of such an event would be like that of standing straight up with your arms in front of you and falling forewards. Try it. Try falling forewards from an upright position and land horizontal, landing and "receiving" the fall with your arms and hands. That was a crash in 7 km/h.
Now let's say you want to simulate a crash at 15-20 km/h. To do this you would fall forewards in the same way, only this time you would stand on a chair and fall off it. Remember, this is still at a very low speed for driving.
To simulate a crash at 50-60 km/h you would have to fall of a 8 m tall building. To simulate a crash at 80-90 km/h you would have to fall from around 30 m high.
I think I'm going to use a seatbelt next time I'm in a car.