Cars required to crash or roll over for a spectacular movie or TV scene are strengthened inside. The stuntman also wears a safety harness, padding and a crash helmet, provided he will not be seen.
When a car has to be rolled, it is either driven up a ramp out of camera shot, or it has a hydraulic arm which shoots out beneath and forces it over. Some of the more spectacular crashes are so dangerous that a dummy replaces the stunt driver. In these scenes, the cars can be catapulted by an air cannon, a device like a giant air gun welded to the rear of the car.
The device was used in Grand Prix (1966) in a scene in which a car plummeted into the sea. A camera was mounted behind the driving wheel and dummy hands fixed to the wheel completed the illusion.
Picture Credit : Google