What immediate action must a bus driver take if the pneumatic brake system warning buzzer sounds and reservoir pressure drops below 6.0 bar while driving?

1. Continue driving at high speed to build compressor pressure from engine RPM
2. Safely bring the bus to an immediate stop off the active traffic lane, as braking power is critically compromised
3. Pump the brake pedal vigorously to manually pressurize the lines
4. Shift into neutral and coast down the road to save fuel