I'm genuinely curious about this too. In my uninformed opinion, for a car that's heading toward an obstacle (e.g. car, truck, pillar, wall, lamp post) there are

I'm genuinely curious about this too. In my uninformed opinion, for a car that's heading toward an obstacle (e.g. car, truck, pillar, wall, lamp post) there are a few possibilities: 1) heading straight while braking: probably the best case as you have the collapsible trunk between you and the obstacle, and you can reduce the speed, if by little; 2) spinning without control and crashing with the back or the sides: worse than 1), but not so bad as there are side airbags and the headrest. The car is at least somewhat protected on all sides, plus there's some tire friction for reducing the speed; 3) rolling over: less friction as the car is rolling, plus the car may crash into the obstacle with the car's roof or floor. Both are certainly more than a layer of tin, but not as protected. Plus, objects flying around the car and limbs in an unsafe position when the crash happens.