Arlington County is planning a rebuild of the Boundary Channel Drive, Interstate 395 and Long Bridge Drive interchange, which is located just east of the Pentagon. This rebuild will include shared use paths along both sides of Boundary Channel Drive with connections to the Mount Vernon Trail, via the stub "Pentagon Lagoon Trail" built in 2011 as part of the Humpback Bridge project, and to Long Bridge Drive and Long Bridge Park.
In June of 2015, they held a public information meeting and released three design concepts and since then the project has been
]working through a Federal Highway Administration/Virginia Department of Transportation technical analysis known as an Interchange Modification Report (IMR). This report will include a technical model to test a number of design concepts for the interchange and ultimately lead to a preferred alternative for this important transportation gateway to Arlington County.
It's not clear how soon the IMR will be completed, but it does appear that their is now a preferred design as recently reported to the County Board.
East of I-395, the preferred concept uses Concept 1 and west of it it uses Concept 2 except on the far west end. On the west end, the preferred design has no trail on the south side of Boundary Channel (west of the Pentagon Access Road) and on the north side, the trail stops a few feet shorter - at the driveway along the Pentagon Lagoon.
The path will have a design speed limit of 18mph.
Design of the fully funded Boundary Channel Drive Interchange project is expected to begin in 2017, with construction forecast to start in 2020.