How should a driver use the vehicle's engine and gearbox when descending long, steep mountain grades?

1. Shift into a lower gear to utilize engine braking (kočenje motorom), avoiding continuous riding of the footbrakes
2. Shift into neutral and coast with engine idling to save fuel
3. Keep the footbrake pedal pressed continuously all the way down the mountain
4. Turn off the ignition switch to shut down the engine