Final answer:
Before driving a truck or bus with dual air brake system, the pressure in each system should be at least 100 PSIa to ensure the brakes work effectively.
Step-by-step explanation:
Before driving a truck or bus with dual air brake system, the pressure in each system should be at least 100 PSIa.
This requirement ensures that there is sufficient pressure to activate the brakes effectively. If the pressure is lower than the specified amount, the brakes may not work properly, compromising the safety of the vehicle and its occupants.
Therefore, it is crucial to check and maintain the air pressure in the air brake system before driving a truck or bus with dual air brakes.