What should be monitored to ensure the parking brake is functioning correctly?

Monitoring the air pressure gauge is crucial for ensuring that the parking brake is functioning correctly, especially in larger vehicles like buses that often utilize air brakes. The parking brake in these vehicles typically depends on air pressure to engage and disengage properly. If the air pressure drops below a certain level, the parking brake may not hold effectively, which can lead to safety issues.

In addition, the air pressure gauge provides real-time feedback about the system's pressure levels, allowing the driver to assess whether the brakes are functioning properly before operating the vehicle. Adequate air pressure is necessary for both the effective operation of the parking brake and for the overall safety of transporting students. Other options, while important for different aspects of vehicle operation, do not directly relate to the functionality of the parking brake.