Why would you even isolate the T from Amtrak in the first place, given what an interlocking beast they are on the Providence Line? South Station and Back Bay and Providence all strike me as highly vulnerable given their very low elevation--and they're heavily shared, of course. Moving outside the shared corridor, Amtrak overall in the northeast passes through some extremely low-lying marsh areas around Mystic, CT, and I'm sure other places. A catastrophe there... how does it ripple out to impact T service up the line?