While driving a passenger bus, the Low Brake Air Pressure Warning Buzzer sounds and the red warning light illuminates. What must the driver do immediately?

1. Ignore the buzzer and continue driving at high speed to the next station
2. Pump the foot brake pedal rapidly 50 times while accelerating
3. Safely steer the bus to the side of the road, stop immediately before air pressure drops completely, apply the parking brake, and investigate pneumatic leakages
4. Turn off the dashboard master switch to silence the buzzer