What happens automatically if a commercial truck suffers a total loss of pneumatic air pressure while driving?

1. The low-pressure buzzer/light activates, and as pressure drops below ~4.5–5.0 bar, the spring brake actuators deploy, automatically locking the rear wheels
2. The truck continues coasting with no braking resistance until running out of fuel
3. The gearbox automatically shifts into reverse gear
4. The steering wheel unlocks and spins freely