A 47L train heads across the Panhandle Bridge as it sets out on its long journey to the edge of the earth, which in this case is Library, at the southern border of Allegheny County. In rush hour, all routes except 52 (the Allentown Trolley) run two-car trains like this one, made up in this case of two CAF cars. The rear car acts as a trailer; it has no driver, and its doors open only at high-level platforms with fare booths, not at street-level stops.
The Panhandle Bridge was originally a railroad bridge; in the 1980s the streetcars from the South Hills were diverted over it (they used to come in by the Smithfield Street Bridge) when the new subway opened. (Part of the subway reused the old railroad tunnel that had taken trains from the Panhandle Bridge to Penn Station.) Since the cars come out of the Mount Washington tunnel right at the end of the Smithfield Street Bridge, diverting them to the next bridge over required an extraordinarily sharp curve at Station Square. But sharp curves are just one of the challenges a trolley has to pass before it’s good enough for Pittsburgh.