If a car's braking system fails completely, what should the driver do?

Pumping the brake pedal rapidly is a recommended action in the event of a complete braking system failure because it can help build up pressure in the brake lines if there is still some residual hydraulic pressure available. This technique may allow the driver to regain some braking control, which could be crucial for slowing down the vehicle or stopping it safely.

In emergency braking situations, it's important to act quickly while also maintaining control of the vehicle. The pumping action increases the chances of stop or at least slowing down, as compared to other methods that might not be as effective under severe conditions. Shifting to high gear, for instance, may not provide the necessary stopping power and could even worsen the situation if the vehicle begins to speed up. Using the handbrake can also be tricky, as it could cause the vehicle to skid if applied suddenly or too harshly. Turning off the engine might cause a loss of power steering and further complicate handling the car, especially if the vehicle is still in motion. By focusing on pumping the brake pedal, a driver is more likely to avoid a catastrophic outcome in a brake failure scenario.