> Air brakes on trucks run in reverse. Compressed air releases spring pressure therefore releasing the brake. I think pneumatic brakes almost universally work

> Air brakes on trucks run in reverse. Compressed air releases spring pressure therefore releasing the brake. I think pneumatic brakes almost universally work this way, because it's fail-safe w.r.t. line leaks. E.g. in trains the main air line is for powering pneumatics as well as releasing brakes; at nominal pressure (8-10 bar iirc) the brakes are released, at lowered pressure (3-5 bar) the brakes are fully applied. If the line ruptures or the train splits all brakes across the train are fully applied.