ATS is tied to the signals. Anything less than clear triggers a response in the engineer's alerter. All the engineer needs to do is respond by hitting the button. Inert inductors placed ahead of slow curve act the same way, demanding a response by the engineer.

No response and a 'full' application of the brakes apply. Suspect some engineers can hit the alerter in their sleep. All this is little help if the signal was red and you just passed it.

The engineer on Santa Fe 3751 is never alone, so I doubt if he will fall asleep. Usually a crew in the assisting Amtrak diesels too. Don't know if 3751 has the any deadman features like current diesels or if it's just a deadman's 'pedal'.

PTC is supposed to stop the train before passing the red signal. Easy concept. Tough to do.