If Mr Curtin is right, that the NEC is crossed on a bridge by the Anacostia line, the next question is, Would the auto racks fit through the Howard St Tunnel, and, if not, is there a reasonable bypass available? If there is a bypass, it seems that the train could terminate near Phila without having catenary problems.
OK: interesting Mr. Curtin that the B&O X'd the PRR on a bridge and not at grade. That means the service could extend as far North as Phila on B&O rails eithout interference from anybody's caternary.
As I recall, the interchange between B&O and RDG was simply a lineside "stick in the ground' somewhat North of the "B&O Station" in Phila which was on the East side of the Schuylkill @ Chestnut Street.
Must confess, even I, @ age 64 and having been in Pilia while the Royal Blue line was in business, never observed the station "in living color'; all I do know is that, when compared with 30th St and Broad St, one "definitely knew' the B&O was the "orphan kid' in town.