Well, the details are application-specific, yeah. The metrorail problem could have been "solved" by making the system refuse to allow a train to travel on trac

Well, the details are application-specific, yeah. The metrorail problem could have been "solved" by making the system refuse to allow a train to travel on track that didn't have a currently working train sensor, but such failures are so common in the system that the whole Metro would grind to a halt, from my reading this summer about this problem (mostly while on the Metro, fittingly).