You look at good copies of the Darnell/Martin Films and BEHIND that 1 Glove DPD Cop, you can clearly see that railroad spur that ran behind the TSBD and stretched across the Elm St Ext. This landmark establishes that this alleged DPD Cop is firmly on the Elm Ext and WALKING toward the TSBD Loading Dock. You even get a brief look at a portion of that same loading dock.
Again, Old Elm ends at the Pergola. Anything beyond that to the west is (well, was at the time) private property, and not a public roadway. The rail yard begins where the bricks end.
Think of it this way, and you've kind of answered this yourself: you noted that there is an RR spur running across the way. If there's a spur line there, you're in a rail yard.