PTS could have prevented it - more or less (assuming we ever get PTS to work right 100% of the time). Up until the point where the calculated braking distance (at whatever speed) exceeds the distance remaining to the target point (the restricting signal), PTS would have allowed the train to proceed being governed by the previous signal.

But as soon as the calculated braking point was reached (or closely approached), either the engineer stops applies full braking at that point, or the PTS will - stopping the train BEFORE the signal is passed. That is because there is still adequate braking distance to the signal to do so.

However, I said "more or less", because of what can happen next. After the enforced stop at a restricting signal (or a non-absolute), the PTS must then permit a restricted speed movement into the already occupied block ahead; simply because that is what the aspect is conveying.

This is where even PTS cannot help much. It has no means to tell whether the crew actually observed switch positions or not - nor can it tell if the crew has taken note of a train or obstruction ahead. Worse yet, PTS cannot do these things for the crew anyway, as no means to reliably detect the exact position of any parked (or unequipped) vehicle has ever been invented. Moreover, a couple-up move under a restricted aspect must be allowed in any event. And that can still lead to a "Hard Couple!"

So PTS will be of no help whatsoever when running on a restricting aspect, except for the initial stop and proceed part of it.

OPB