It will be limited though. Mostly single track line. There is a siding right after the Charles River Bridge and that ridge can be upgraded to a double track because it once was. Single track would have to be kept in the MIT area because the tracks go through buildings. Plus they will have to combat with the roads and make sure that Mass Ave does not become bumper to bumper. (Reason why all MBTA/Amtrak shifts over the Grand Junction are at night or the early morning.) New switches must be installed to allow fast trains over the line. Plus what is now Beacon Park will have to be upgraded to at least two or three main line passenger tracks instead of one because there is no way to get off that track to the Grand junction without going throught the what is now yard. The switches are near the Market St. Bridge. It would be interesting just will take work.
I'm glad the Lieutenant Governor is so enthusiastic, but my Google-Earth-surf showed a half-dozen grade crossings between but not including Storrow Drive and O'Brien Highway, not to mention numbers of informal pedestrian shortcuts. Does the plan include grade separation to deal with vehicular and pedestrian traffic? Elevation would be more than expensive, as would depression, which has the additional complication of infiltration from the Charles and the former navigation canals east of MIT.
Thanks, Tim, for giving us something to post about -- Big Dig II-The Sequel. In a way it does make more sense than tunneling yet again under Boston. Mebbe AMTK might also see some gain out of it, like ending the orphan status of The Downeasters. Reformat the northside approaches, reformat the southside approaches, deal with capacity issues, and The Hub could become something other than a segmented wheel.