There is a significant redesign of Columbus Circle in the works. See this write-up:

http://greatergreaterwashington.org/post.cgi?id=892

Among the changes will be re-directing all bus traffic around the back of the station (as is already happening with the Circulator buses. However, it is unclear when work will begin on this redesign. My impression is that funding is not yet authorized. The delays in constructing the bike station -- largely funded by a Congressional earmark -- do not encourage optimism.