What is the maximum allowable air loss in a straight truck or bus with the engine off and brakes released?

Answer: C — 2 psi in 1 minute

The maximum allowable air loss in a straight truck or bus with the engine off and brakes released is 2 psi in 1 minute. This standard is set to ensure that the vehicle's air braking system maintains sufficient pressure for safe operation. When the engine is off and the brakes are released, the system should not lose more than 2 psi in one minute, as excessive air loss could indicate a leak in the air brake system, compromising braking performance and safety. Maintaining this threshold helps drive operators to recognize the importance of routinely checking their air systems for leaks. If the air loss exceeds this limit, it would necessitate further inspection and possible repairs to ensure the vehicle remains safe for operation on the road.