Any day now, if the schedule at this site is correct, Arlignton County should break ground on a project to improve the highway interchange at Route 50, Courthouse Rd, and 10th St. In addition, this project aspires to improve the bicycle/pedestrian path that runs through the intersection (often as simply a sidewalk).
According the the Arlington County site, this project will include a new trail along the south side of Arlington Boulevard (US 50) from N. Pershing to Rolfe Street. The south side would be the Fort Myer side, but based on the description and photos, I think that's a mistake. I think they mean the north side (and the west side). Which means the project will improve the existing path/sidewalk. Update:As noted in the comments, this project includes a new trail on the south/east side AND an improved trail on the north/west side. Both trails will be 10' wide.
A bicycle trail will also be added eastbound on Arlington Boulevard from Pershing Drive to Rolfe Street. The existing trail on the westbound side will be relocated to parallel the C-D road and will be extended under the 10th Street bridge.
The trail currently stops at Courthouse and does not go under 10th. This project will connect it to the existing Arlingtion Blvd Trail that currently ends at Pershing. There are a lot of goodies for cyclists and pedestrians in this project. I don't know how in snuck past me for so long.
As you can see in the image below, it looks like the Courthouse road underpass will have the trail widened, raised above the road, separated with a guardrail and will include grass borders. Not bad.
The next rendering shows the trail north of the spot above. The trail looks wider than the current one, and it appears to have its own lighting.
According to the schedule, construction was to begin in March and take 30 months. (Helmet tip). Update: VDOT has it starting in April and ending in October 2011.