In an extreme emergency where a taxi's service foot brakes suddenly fail while descending a steep mountain road, what sequential emergency steps should the driver execute?

1. Turn off the ignition switch immediately and lock the steering column
2. Shift down progressively through lower gears to use engine braking, gently apply the parking brake in controlled pulses, look for emergency escape ramps, or rub against natural roadside friction barriers if necessary
3. Jump out of the moving vehicle immediately
4. Shift into neutral and let the vehicle coast freely