There was one a decade or 2 ago called the urban ring project, but it got cancled because of a lack of funds. It got partially implemented, the SL3 to Chelsea is the only piece of the plan to ever get built. Shame it got cancled, it woulda made 8 new crosstown bus routes, 2 express commuter routes, 6 BRT routes forming a circle around Boston, and some new rail service from assembly sq to Nubian sq via east Cambridge. But hey, 2.8 billion for a rapid transit scheme that would add 300k new riders each day, 42k of which would be converted from cars, is an insane deal when you can spend 20 billion on the big dig, a highway project that ended up being a great example of induced demand