NYCRRson wrote: ↑Mon Aug 14, 2023 3:33 pm
"Pure speculation: Could it be that the switch changed positions while a train was on it?"
The turnouts in an interlocking are mechanically locked by the switch machines. The turnout is not going to "change position" without a command from the computer controlling the interlocking. And that computer will not change anything in the interlocking when a train is approaching, in the interlocking, or leaving the interlocking.
The wheels / axles / trucks of a train car could fail and break the turnout parts and force them into the wrong position during the derailment. So a first look at a turnout after a derailment might look like it is in the wrong position, but it could be a result of the wreck and not the cause.
The machines themselves are what hold the points against the rail. The computer is what tells the machines what to do after a few clicks of the mouse by the dispatcher, RTC, operator or what ever they wish to call themselves. Interlockings were once mechanical hence the name, where levers and rods interlocked to set a route. Same idea here just done by the computer in Jacksonville FLA..
They can not change switch position as a train approaches or goes through the interlocking. The route is set and locked. If something were to happen inside the interlocking before the train was to arrive at that location the signal system would default to stop as would the I-ETMS.
It would also show on the dispatchers screen that something was up inside the interlocking. Conversations would be had because he knows what he did and he wants to know what happened in the field. Everything we do be it T&E or dispatchers is on "tape".
As for the signal system, the dispatcher can not clear a route until the train shows clear on his board and it unlocks the interlocking. Or if he stops a train before it enters into a interlocking by A. asking if train XYZ can stop before entering and B. asking to take away the signal once train XYZ is stopped. You might hear I gotta run down the signal or time it out in the conversation. Because back in the days of mechanical interlockings there was a actual timer 5 minutes or so before you could change a route. A built in safety precaution.
There is a brief lesson in railroad interlockings and how they work. CSX calls them CPs or control points its all basically the same premise. Just have to know which railroad your on which rules to follow.