Well, We ran ALL Amtrak service over that route for the 8 years it took to build the Southwest Corridor. I would presume my proposal would entail the same improvements for the Fairmount Line that the SW Corridor experienced when it was re- built. I ran freight and passenger service over the Fairmount Line so my evidence is my recollection of the route. And my proposal includes electrifying the T service too. That would help to increase the average speed over the route. And I am all for increasing capacity on the SW Corridor too! Further. I think getting thousands of people to work faster each day ( Franklin service at Ruggles and Back Bay) Is a higher priority than the extra 10 minutes it might take to catch the Acela out of South Station than at Back Bay.
It doesn't matter. Amtrak controls the dispatching on the NEC. They maintain all the track, maintain all the electrification. They like the ticket revenue that Back Bay provides. No force--not even MassDOT--has the power to compel them to make a move to inferior environs when they don't want to. Either show a reason Amtrak would
want to do this, or admit it's a God Mode personal preference. Amtrak isn't going to choose the Dorchester Branch of its own volition...and Amtrak's own volition sets the table here.
Especially when the ride to South Station from Readville is already 15 minutes longer via Dorchester than Readville to Back Bay via NEC. Even with a immediate departure, cross platform transfer, Readville to BOS to BBY is a 20 minute longer trip in the best circumstances. That is a tough sell to Franklin Line riders. Far better to convert Needham to OLX/GLX2 and leave Franklin alone.
Franklin can't be "left alone" and get Regional Rail frequencies. :30 minutes bi-directional clock-facing won't mix with :30 bi-di Providence, :30 bi-di Stoughton, and all of Amtrak + future Amtrak growth. Not even with Needham expunged (though it's that much worse if Needham
isn't expunged). That's how serious the SW Corridor capacity crunch is.
So some enhanced usage of the Fairmount Line is mandatory if you want to give all of these lines (at least Providence + Stoughton + Franklin) equitable turns in a Regional Rail universe. The T
can guarantee :30 bi-directional clock-facing frequencies by running all Franklin + Foxboro service over the Dorchester Branch. There's no Amtrak traffic complicating the mixture, and the T is the dispatcher for Fairmount unlike the NEC which is Amtrak-dispatched. So that's why they put moving Franklin over to Fairmount in the Rail Vision documents as a bucket list item.
The reality is a little more granular. Yes...you have to use Fairmount more often to prop up the backside of a Franklin Regional Rail schedule and do so without gapping out the clock-facingness of the frequencies. You
don't, however, have to use it exclusively. Backfill slots will be available via the NEC. They just may not conform to the same clock-facing intervals, so you have to pick your spots. It probably won't be as full a slate as currently runs NEC-Franklin, but it can be a plenty useful number of BBY/Ruggles slots. So long as they don't infringe on clock-facing Providence or Stoughton/South Coast slots that have first priority for the NEC there's a lot of leeway for portioning the schedule, and nobody gets deprived of access.