Would Automatic Train Stop ( for example, the Santa Fe's Intermittent Inductive Train Stop ) protect against head-on collisions ? Would it have protected against the sort of collision discussed here ? Would cab signals, either alone or in concert with ATC or ATS have prevented this sort of event ?
Let me first preference my reply with the disclaimer that until all the facts are revealed in this accident by the NTSB, some if not all of what I say, could be invalidated.
ATS cannot prevent head-on collisions.
And in this specific case I see nothing that suggests that it would have changed the above statement and would not have prevented the collision. It might however have reduced the closing speed between the two trains, and therefore have lessened the severity of the collision and quite possible have saved some if not all lives.
As for whether cab signals would have helped, that we will probably and sadly never know. Since we don't really know what happened inside that engine, its mere speculation to talk about this. But if indeed the signal wasn't as bright as it was supposed to be, or if indeed as several claim the signal was showing clear, then assuming that in between his text messages Mr. Sanchez had glanced at his console, he might have realized that something was majorly wrong and stopped his train before crossing the switch.
If the cab signals were working in concert with ATS, then he'd have a rather loud horn blaring in his ears to distract him from his text messaging once he passed the red signal. Again, that would have given him time to slow and perhaps even stop his train prior to being hit by the freight, but I would think that a collision still would have occurred. It's highly unlikely that he could have radioed the UP train fast enough for them to start stopping prior to hitting him. But again, it certainly would have decreased the closing speeds, maybe 40 to 50 MPH, and probably saved lives.
Had he failed to acknowledge that horn and deal with things, ATS would have eventually kicked in and started stopping the train. But those extra seconds that the ATS system would have given him to take action would have been critical. By the time ATS started braking, I’d guess that they would have been mere seconds away from the collision. Again, every MPH slower is a help, but I’d guess that closure still would have been in the 60 MPH to 70 MPH range.
With PTC in place however, the computer would have started demanding that Mr. Sanchez take action to slow the train as he approached the signal prior to the switch. If he didn’t, it would have begun slowing the train itself long before it got to the signal. It’s unclear if the train would have stopped prior to crossing the switch, as there are too many variables in that equation since there is no system in place and we don’t know what parameters might get set for the system.
Additionally had the commuter train still crossed the switch, the freight crew would have received an immediate warning that something was in its way and they too could have applied their brakes rapidly. Again, I suspect that with the distances involved here that an accident might still have occurred, but it would have been a low speed event with maybe a 15 to 20 MPH closure rate, instead of the near 80 MPH rate experienced.
