> There probably is trackage that wont take it tho.
> Like when the RDG2100 derailed!.


That had nothing to do with the condition of the track, it was in good shape.

The problem was simply the curvature at that location. You can't take a 4-8-4 around a curve that's something like 20 degrees. If you do try, something will eventually give.

Since TR never anticipated having 4-8-4's wandering about the property, there was nothing in the special instructions about "Do not take 4-8-4's around these curves" so the TR train crew didn't know any better and wasn't breaking any rules when they attempted that curve. It was a unique situation that nobody anticipated.