When parking the bus, what should be done to the air pressure system?

When parking the bus, it's essential to properly manage the air pressure system to ensure safety and prevent potential accidents. The correct procedure is to decrease the air pressure until the parking brake knob will no longer stay in. This action is crucial because it ensures that the parking brake is fully engaged, providing security to the vehicle when it is stationary.

The parking brake on a bus operates using air pressure, and when parked, it must be set correctly to prevent the bus from moving unexpectedly. By lowering the air pressure to the point where the parking brake engages, the driver ensures that the bus remains safely in place, thereby reducing the risk of accidents caused by unintended movement.

Other options either do not address the engagement of the parking brake effectively or may compromise safety. For example, simply leaving the pressure as is does not guarantee that the brake is engaged, and increasing pressure would only make it challenging to set the brake. Draining all air pressure is not a viable option, as it would release the parking brake entirely, posing a significant safety hazard.