Arnold D. Cribari posted:Lew, I think your post is interesting and has merit. But isn't the defective track for real trains typically on sidings and rarely used trackage where trains would go slow?
In my experience in observing real trains and track, which is quite limited, high speed frequently used main lines have track that looks perfect.
Do you folks agree?
Yes, of course mainline track has to have very good alignment. Maybe one of the "real" 
railroaders here will chime in with a short summary of FRA track specs.
As a general statement, track condition determines the FRA allowable speed on that track. IIRC with deteriorating condition it gets down to 5mph and then finally the track is embargoed. I know a bunch of specs go into the determination, among them the condition of the ties, what % of ties are in what state of health, how many spikes are missing, whether spikes are fully driven, the profile of the railhead, missing/loose track joint bolts, track gauge as well as the actual alignment of the rails.
I have walked a lot of "bumpy" branchline track, especially if it is jointed rail having "low joints and high centers". Not uncommon (on slow-speed track) to see a 2" gap between the underside of the rail and the tie-plate for a couple ties at the rail joint. I find it a bit disconcerting to stand beside such a rail joint when a train passes over it and watch the weight of the wheels flexing the rail down to make contact with the tie plate and then springing back up when that wheel has passed.
