Virtually ever location where there are crossovers can be used to turn trains
Except that about half of them are programmed in the codes, and as Oren (was it Oren? Might have been Mountain Mark) said, they typically don't use crossovers for turnbacks except at end terminals, because they'd need to hold the train either before entering to drop off, or before depatring to cross over, which might tie up end-to-end movements. I would mention that SEPTA has no problem using crossovers for tunbacks, but tha'd be inaccurate. The Regional Rail trains typicaly have yards or four+ track ROW where this is done, and the one instance in which the BSL does it is at Walnut-Locust for expresses... which layup on the partly extended Express tracks (which stub end just shy of Lombard-South Station) before/after crossing over. The MFL NEVER, EVER does this, unless ALL trains are turning back there for some reason (Frankford guideway rehab, FTC, upcoming Market St rehab (will terminate trains at 40th Street)), and the sole pocket track the line has sits IMMEDIATELY inbound of one station, so it's not too clear what it'd be used for.
If you take away the platforms at National Airport (C10) and West Falls Church (K06) you have a pocket track. As far as I am concerned both National Airport (C10) and West Falls Church (K06) are pocket tracks, West Falls Church (K06) is a surface station.
Thank you. Hm... if you DID remove NA and WFC's platforms, then East Falls Church and Crystal City would have pockets for terminating trains... albeit, in a very wide space. Blue occasionally (more like "rarely") terminates at NA and Orange occasionally at WFC... do Yellow trains ever short-turn at the Airport also?