Is main reservoir air pressure train lined on M-3/M-7 trains?

The main reservoir air pressure on M-3 and M-7 trains is not specifically "lined" or connected to show a direct link that is visible or manipulated on the dashboard like some systems. Instead, the air reservoirs operate independently to maintain pressure for the brake system across the train. This is a standard feature in cab signaling systems, where the air reservoirs ensure that brakes are applied correctly and reliably without being dependent on a directly indicated line.

The design and operational protocols for these trains generally mean that the primary function of the air reservoirs is to manage air pressure for braking, rather than being monitored in a way that implies a continuous connection as "lined." Understanding this is crucial for operators and maintenance personnel to ensure that air brake systems function correctly under various operational conditions.