bramling
Veteran Member
The passenger alarm isn't linked to the brakes but the emergency egresses on the doors are. The driver has the ability to isolate the interlock circuit to proceed with no door interlock but how do they confirm that every set of doors is closed before doing so? This is what happened at the Kentish Town stranding a few years ago.
Traditionally I believe you could release the brakes with no traction power - not sure if this was with a purely pneumatic system or an electrically actuated system which would need power from batteries. However someone mentioned upthread that this modern trains do not allow this. Perhaps there should be an override to allow brake release if there is power in the batteries and enough air in the reservoirs to be able to stop again?
On most trains you can generally release the brakes and roll, but providing the train still has air (in other words it hasn’t been used up or leaked away - the latter process will naturally vary in time from unit to unit), and providing the battery holds up and crucial circuits don’t drop out. All this also assumes there’s nothing else wrong with the train of course.
What isn’t feasible is to *isolate* brakes, as opposed to merely *releasing* them. The critical difference is that in the first instance it’s not readily possible to re-apply whereas in the second instance it is. There are things which can be done in extreme defect scenarios involving isolating service brakes and relying on parking brakes, but this would only be done under extreme circumstances and under controlled conditions - absolutely no chance with passengers still on for a start.