Planners have mixed ideas on Rt 1 - some want it to be a major commuter corridor, others want it to become a mixed-use walkable community. The two visions are ordinarily incompatible (fast traffic kills pedestrians), but there is a way to satisfy both: (1) extend Yellow Line (underground) to Ft Belvoir (or, preferably, to Lorton or Woodbridge) to reduce overall traffic count; and (2) build traffic tunnels (like Dupont Circle) or, where appropriate, above-ground decking (like the decking in on I-66 at Rosslyn primarily for pedestrians and businesses) at designated CBCs (i.e. Penn Daw, Groveton/Beacon, etc) so traffic can continue moving at those places while allowing for mixed-use/walkable/urban village development at the same time. Part 2 can be competed well in advance of the metro extension, and can work even if the metro extension never happens.
Idea No. 5