Completely rebuild the Southeast Expressway with a two-level setup. Ground level would be 4 full travel lanes in each direction with a full shoulder on each side, each direction. In the middle would be two full travel lanes with full should in each direction - this would be a tolled express lane inbound. Underground, you would have two full travel lanes, with a full shoulder in each direction and this would be a tolled express lane out bound. You'd also have space for dedicated tracks for the red line to allow express trains to run into SS and avoid North Quincy, JFK/Umass and the crawl that exists for the stretch from Savin Hill through the tunnel to Andrew.
Roughly around Neponset Circle, you would have a dedicated airport tunnel built that would be fully submerged and have 3 full travel lanes in each direction, with full shoulders on both sides, both directions. Tunnel would run under the harbor.
This isn't really a crazy pitch, but completely expand and rebuild the 93/95 interchanges in Canton and Woburn, the 93/24 interchange in Randolph, the 90/95 interchange in Weston, the 95/3 interchange in Burlington, the 495/95 interchange in Mansfield and the 495/90 interchange in Hopkinton. Widen route 3 to 3 full travel lanes, plus shoulders, from Derby Street all the way down to the Cape.