The Office of Planning has a public realm plan for the area, which includes two-way streets on New Jersey and Fourth, some narrower intersections, better landscaping along the streets, reconnected L and 3rd streets across I-395, and a Neighborhood Center plaza at 5th and K.
The Triangle wonders if cutting the freeway back would simply generate traffic through the neighborhood to the Mass Ave ramps. It’s possible, but we should also remember the principles of induced demand: adding road capacity induces more traffic by encouraging driving; removing road capacity does the opposite. Removing the appeal of a through route here, especially given alternatives, would most likely reduce more traffic than it reroutes.
And I can think of a great use for a long, narrow, below-grade trench running between M and K Streets: the separate Blue Line, which I guessed might run under New Jersey Avenue. But why not save a bunch of money and build that segment where the highway now sits? Coming along M from the Convention Center station, it could tunnel under New York Avenue, break into the existing I-395 trench, stop at a station around K Street, then turn off at H Street just north of where the freeway would now begin at Massachusetts Avenue.
Plus, maybe one day the tracks could replace the freeway all the way under the Mall and down to the Navy Yard area. With many lanes south of Massachusetts, we could even keep lane or two for cars.