Woops I was thinking Balt to DC and the gap you mentioned is the only section on the east coast between Fredricksburg/ Manassas and New London Conn. that doesn't have commuter service with VRE, MARC, NJT, Metro North or Shoreline East.

George Drury wrote a trip up in Trains Mag that he did a number of years ago covering all of this by commuter train, but that may have been VRE started

Bob H