When is an "EL" not an "EL"?

These two photographs taken this morning from a Manhattan bound F train on the "Culver Viaduct".  The top photo shows lower Manhattan as the train is about to enter the Smith-9th Street station which is the highest in the NYC subway system.  The second photo, take a few moments later as the train is going down the incline to the Carroll Street station which is underground.  The "Culver Viaduct" is a concrete covered steel structure which is going under rehabilitation.  The foreground of the second photograph, where you can see green grass, was the former site of large natural gas gas tanks.  Beyond the grass is the Gowanus Canal and the high Smith-9th Street station that goes over the canal.  I believe the former gas tank site is a very toxic site and nothing can be built over it.  The viaduct was constructed in the late 1920's and opened in the early 1930's for the new Independent Subway Prospect Park Line.  The traditional BMT Culver Line, that reached Manhattan by way of the 5th Avenue El and the Brooklyn Bridge or the BMT subway on 4th Avenue and through the Montague Street tunnel, never used this trackage.  When the IND Prospect Park Line was extended to Coney Island via the BMT Culver Line south of Church Avenue in 1954, the line became know as "Concourse - Culver ", but on the old R1-9 equipment, this name was never applied and the train was simply known as the "D" train,  or "Houston Street - 6th Avenue Express" . Only many years later, after 1967, did the rerouted "F" train became know as the "Culver Line".