Alertor unacknowledged will only set up a Penalty Brake application, after the alertor has been active for about half a minute. All of this takes time and distance from the last point the alertor was acknowledged, to the point where the train is actually stopped. The lag time between alertor annunciations is also significant.

And it is just as easy to continue to acknowledge a desk-top mounted alertor mash button in a dream state of early morning doziness as it is driving home drunk off your ass without causing mayhem. Trust me. The Holy Grail of PTS-sponsored fail-safe fantasy land remains to be seen.