The Chain Bridge is the last crossing of the Potomac in the District, and the last bicycle crossing for 30 miles where you can use White's Ferry - but not between 11pm and 5am. (Here's a cool photo of the old bridge, btw). The bridge serves as a connection between Arlington and Fairfax on one side and the C&O and the CCT on the other side. I've only biked across the bridge once - and that was a while ago, so my assessment might not be dead on, but as I recall there is a 4 or 5 foot wide bike/ped lane on the upstream side and one can bike across the bridge in the travel lanes unlike on the Mason or Roosevelt. There's a good connection to the C&O and a bad, unofficial one to the CCT. On the Virginia side a trail connects users to the Arlingwood neighborhood. On both sides the presence of highways and Canals limits movement.
One positive development in the area could be the expansion of the Mt. Vernon Trail north. A study on such an extension was performed by the park service in 2002, with no progress yet, but it would help to expand options for those traveling between Virginia and D.C. (map)
1. Build the Mt. Vernon Trail extension.
2. Formalize and improve the connection between Chain Bridge and the CCT. Due to the steepness of the slope this may require steps, but it could still be improved. An improved crossing of Canal Road is needed as well (grade separated or otherwise)