Final answer:
The correct air leakage rate for a combination vehicle with the engine off and brakes on should be less than 3 psi per minute to ensure proper brake system function and road safety.
Step-by-step explanation:
The air leakage rate for a combination vehicle (engine off, brakes on) should be less than 3 psi per minute. To clarify, in the context of commercial driving and vehicle inspections, it is important to ensure that the air brake system maintains pressure effectively to guarantee safety on the road. If the air leakage rate is too high, it can indicate issues with the braking system that could lead to brake failure or reduced brake effectiveness.