Which air pressure is train lined on M-3/M-7 cars?

The air pressure that is train lined on M-3/M-7 cars is the brake pipe pressure. This pressure is critical for the operation of the air brake system, as it is used to communicate brake commands between the train cars. When the engineer applies the brakes, the brake pipe pressure is reduced, which then activates the brakes on each car in the train.

The brake pipe serves as the main conduit for transmitting the brake signal, ensuring that all cars receive the same command to slow down or stop. The system works based on the principle of graduated release and application, where a change in the brake pipe pressure results in proportional changes in the braking force throughout the train.

Understanding this pressure’s role is essential for safe and effective train operation, as it directly impacts how quickly and smoothly the train can respond to braking commands. The other pressure types mentioned, while important in their contexts, do not serve the function of transmitting brake commands across the train.