[crottypeter]

Yes, that is what the crumple zones are for!

Not sure what you mean by this: > pushed from the back with rapid acceleration, or absorbing the energy of a collision. The occupants don't have to absorb the impact if the crumple zones take it!

I guess decent seats will do a lot to protect the occupants. A few years back I was a rear-seat-passenger in one of these https://upload.wikimedia.org/wikipedia/commons/5/50/Nissan_M... when it was rear-ended. Luckily our driver WAS on the brake and didn't go forward into the cars in front - unlike the car behind us and the car behind them and the car behind them! (I forget exactly how many cars were involved but it needn't have been as many).