Which system is primarily responsible for slowing down a train?

The air brake system is primarily responsible for slowing down a train because it relies on compressed air to activate the brakes on each car. When the engineer applies the brakes, air pressure is released from the system, allowing brake shoes to press against the wheels and create friction, which effectively slows down the train. This system is essential for safely stopping trains, as it provides a reliable and efficient means of controlling the speed of heavy rail vehicles.

In contrast, the electrical system is mainly involved in powering electrical components of the train such as lights and communication systems, and does not directly contribute to braking. The signal system is designed to manage train movements and ensure safe operations, providing instructions to engineers but not actively controlling the braking process. The safety system encompasses various features and protocols to ensure the overall safety of operations but does not focus solely on braking functions. Thus, the air brake system is critical for the train's ability to slow down effectively.