JIS, also in the trainorders thread:
The cause of this mishap turns out to be a rules violation, not paying attention to the route running at restricted speed.
When putting this with you quote, assuming they are both true, of course, you see a living example of the norm that it usually takes multiple rules violations to create a disaster. We must say "assuming these statements are true" at this time, because we cannot know for sure that they are as yet. They are reasonable and even likely probabilites, but not yet proven.
If the signal maintainer had cranked over the frog, failure on the part of the engineer to observe the switch and frog position would have not caused the derailment. If the engineer had observed the switch and frog positions as running under restricted speed rules required, he would have stopped short of the frog, so no derailment. It took two screw ups to cause the derailment. Note that they were not by the same person, either.
I have seen a turnout with movable frog in UP tracks that had signs on both sides of the track at the switch point warning that the frog must be cranked over when the switch is cranked over.
Is it possible to know, electronically, that the switch and the frog aren't in sync? If so, someone could have known automatically.
Yes. The issue did not apply to this situation as the operation was supposed to be restricted speed, which means by line of sight, making sure everything is as it should be. (The rule gives a list.)
The basic concept is fail safe. That is if anything fails, the system will not give you clearance to use the turnout.
A normal AAR switch machine has three rods: A drive rod, a lock rod, and a detector rod. Some have two detector rods, one for each switch rail. If these three (or four) do not agree, then a clear signal cannot be given across the switch. For turnouts with multiple switch machines, and for crossovers, for the turnouts on both ends, all switch machines must be saying that their switch (or frog) is where it ought to be for whatever the move is supposed to be before a clear signal can be given. This is the meaning behind the common term, "Interlocking" In essence an interlocking system says that conflicting moves cannot be permitted by the signal system, and also that the arrangement of all switches, etc is set so that the permitted movement can be safely done.
The rods do exactly what their names imply. The drive rod moves the switch points. The seperately attached lock rod is moved by the switch. If it is not properly positioned, the lock cannot close, so no clear signal. Once locked, it holds the switch point in place, power or no power, and stops any attempt to move the switch. The detector rod is also moved by the switch rails, and its proper position closes a circuit indicating the switch position. The system is very difficult to defeat. I do not know how, and would not ever say how if I did find out.