Elon Musk is making noises about a DC-NYC "hyperloop" with stops in Philly and here in Baltimore. Best of luck to him, I suppose - maybe in fifty years or so the Sprawl will be an actual thing.
The Northeast Corridor is one of the few places in the US where density makes ambitious rail projects viable, at least on paper. Of course, that same density makes them extremely challenging to imagine actually building. Just the current tunnels into NYC are a real issue right now.
