The X-Codes, as they are known in Arrow, are OS locations along the route. XFL is actually considered "Florence Tower". XLO is "Lorton Switch". The list goes on and on.
CrewDorm -- Does this mean that ARROW is the only system Amtrak has for keeping track of its trains? How about on the track that Amtrak owns? Do they base their dispatching on Arrow or do they have another computer system for that?
Edit: With some Googling I answered some of my questions. See if this is at least rougly correct On Amtrak owned road, CETC runs all the signals automatically and all the signals are connected to the CETC computer by fiber optic (except for a few places that are still dispatched manually).
So then, do Arrow and CETC inter-communicate? Ie. does Arrow get its train status info from CETC automatically? I suspect not, that instead even on Amtrak owned road, the station agents have to manually enter the train arr/dep info.