What information is provided by an air brake gauge indicator in the cab?

An air brake gauge indicator in the cab provides real-time air pressure levels in the braking system. This information is crucial for the operation and safety of the train since proper air pressure is necessary for the brakes to function effectively. Understanding the air pressure allows the operator to ensure that the brakes are properly charged and in a working condition before starting or during operation, preventing potential failures that could lead to accidents. Monitoring this gauge helps train crews to assess the system's status at any given moment, which is vital for maintaining safe braking performance.

The other options relate to different aspects of train operation but do not pertain to the specific function of the air brake gauge. Speed, distance traveled, temperature of components, and cargo weight are all important for overall train management, yet they are monitored through different instruments or systems in the locomotive.