Okay, I was assuming a failure in front of the train. If the failure is behind the train, it's still an extremely solvable problem. Blast gates to stop the in

Okay, I was assuming a failure in front of the train. If the failure is behind the train, it's still an extremely solvable problem. Blast gates to stop the inflow of new air. Or inject air in front as nickparker suggested. I don't see that this is a legitimate blocker to this technology.