What is one sign of a failing air brake system?

Increased stopping distance is a clear indication of a failing air brake system. When the air brake components are not functioning properly, whether due to air leaks, worn-out brake pads, or issues with the compressor, the brakes may not engage with their usual effectiveness. This means that more time and distance will be required for the train to come to a complete stop. In rail operations, where safety and timely stopping are critical, an increased stopping distance could signal that immediate maintenance or repair is necessary to prevent accidents and ensure safe operations.

The other options, such as vibration during driving, steering wheel stiffness, and reduced engine power, may relate to different mechanical issues not specifically tied to the air brake system. Vibration might indicate problems with the wheels or tracks, steering stiffness could suggest issues with the steering mechanism, and reduced engine power typically points to drivetrain or engine performance issues rather than brake functionality.