Mystery Thing I Don't Know What to Call-- September 12th

Merion Avenue Thing

4900 Merion Ave

What the fuck is this?

               Since the railroad-related Lost Mystery Building of the Week last week made such a stir (go read the comments), I'm coming back with another mystery for the rail nerds out there... if this is, in fact, a rail-related structure... I really don't know.
                The Merion Avenue Thing looks like it might have been a bridge... but where's the rest of it? It doesn't appear on any old maps that I can find. From the top, the Thing looks like it might have an accidental green roof:

               So what in the fuck is it? Normally I'd have a more than a few sentences to tell you about something like this, but I can't find ANYTHING. Its like this bridge segment once existed in an alternate timeline and was brought here by some kind of Einstein-Rosen Bridge. My best guess, according to old aerial photos, is that a small line that came off one of the 600 freight lines that once ran parallel to Merion Ave leapfrogged over the northern property and terminated at the southern one, using that bridge to get there. The Chalfont Coal Co. had that spot for quite awhile.. maybe they were the ones that built this thing.
             That's just speculation... for all I know, it could be a bridge-shaped memorial in memory of a turkey sandwich. This shit is just fucked up. Whatever it was, no one ever seemed to have any motivation to demolish it.. and it doesn't seem to be going anywhere. Does anyone know? Anyone?