Lets not get all fancy here. Its supposed to break on a 1/4". Depending on how loose the switch package and track work (loose wedges) and the fact that it's the UP, theres no telling what kind of changes in adjustment happen with the temperature change on that long a$$ bridge.
It happened at the tail end of the crossover on a trailing point move. I've heard some info on it but will not divulge.
So what are you beefing about? The technical explanation? So what. If a switch circuit controller of any type is out of adjustment, locking and indicating correspondence on a 1/4" or greater obstruction, and a signal was allowed to clear over it, that's a false proceed. The FRA would be all over that and I've seen no indication that they are with this incident.
But yes, the train was already in a CP on the near track with a RH xover, so that would almost certainly rule out a split switch. Looks like the derailment occurred in the vicinity of the frog. UP has said "mechanical" issues played a role. That makes me think of a broken rail, broken frog, broken axle.
