Sure there are safety considerations (and plenty of dramatic safety events from BART), but I'd venture to guess even there it's rarely quite so black and white.

Sure there are safety considerations (and plenty of dramatic safety events from BART), but I'd venture to guess even there it's rarely quite so black and white. I was actually thinking more of day-to-day nuisance problems than anything else. Things like getting stuck at the station while the train's computer gizmos reboot, stop annunciators getting confused (or out of sync with each other), having to position the train manually within a station. Or even software failures as hardware wears out – shit like that almost always fails in a safe manner. Unfortunately even a safe failure can have massive consequences which raises the cost of failing fast and breaking thing often.