>The problem with existing service is it requires going through South Station or Back Bay which burns a lot of time. If you live in Somerville, for example.

That's inevitably true of transit routes - they're built where the peak demand is.

We're yet to even get our act together to have one cross state rail service that runs more than at most once a day and that only as part of the Boston split of the water level Chicago service.

Actually building one beats musing about a second.

Note that if you try to drive from Somerville to Northampton you're probably going to take 90 south of the Quabbin rather than route 2 north of it, which is to say, you'll be roughly paralleling the train.