What are the minimum required pressures for the brake pipe and straight air pipe before moving SMEE cars, respectively?

The correct answer is based on the specific operational standards and safety requirements for SMEE (Screw Motion Electric Equipment) cars. The minimum required pressure in the brake pipe of 90 pounds is crucial to ensure that the braking system is fully operational and can effectively stop the train when necessary. A proper brake pipe pressure is essential for safe train movement and handling, as inadequate pressure could lead to system malfunction or failures during operation.

The range of 72 to 80 pounds for the straight air pipe is established to maintain an adequate level of air pressure for the air-operated systems, ensuring reliable performance of the pneumatic components that assist with various functions of the train. This range allows for effective operation while allowing a margin for pressure fluctuations that may occur during regular train operations.

Overall, these specific pressure requirements are rooted in operational safety practices designed to ensure the reliability and effectiveness of the train's braking systems, which are vital for both passenger and freight safety.