What is the purpose of a locomotive's air brake system?

The purpose of a locomotive's air brake system is to slow down or stop the train by using compressed air. This system is critical for the safe operation of trains, as it allows the engineer to control the speed of the locomotive and any attached cars effectively. When the engineer activates the brakes, compressed air is released into the brake cylinders, which then apply pressure to the brake pads or shoes, creating friction against the wheels and causing the train to slow down or come to a complete stop.

This method of braking is preferred in rail transport because it provides reliable stopping power even with heavy loads. The air brake system can be operated from the locomotive or from the rear of a train, ensuring that it can be engaged in a variety of situations while maintaining safety across long distances. Each of the other options does not accurately represent the primary function of the air brake system.