It is interesting to note that since the Metrorail silver line extension to Dulles Airport has moved forward, Maryland officials have started talking about an above-ground green line extension to Baltimore-Washington International Airport (BWI). The convenient excuse for the extension is the military moving more than 5,000 jobs to Fort Meade, a base equidistant to Greenbelt and BWI. There's nothing like a little inter-suburban rivalry to loosen the purse strings.
Metrorail has proven to be a good proposition for the District as it seeks to anchor the metro area and increase property values. I would like to see city officials cement this advantage by building one or more additional lines in the city. Some areas in need of additional service include Georgetown & Wisconsin Avenue, 16th Street/Georgia Avenue from Columbia Heights through Walter Reed Medical Center (which eventually is to be closed and turned over for development to the city), New York Avenue/Rhode Island Avenue through the National Arboretum to Mt. Rainier, and H Street from Union Station through Southeast D.C. There are also opportunities to decouple some lines to make the system more convenient and to increase system capacity.
At about $225 million per mile underground, Metrorail seems to have scared off city officials from further investment, however. In my opinion, the city is not valuing highly enough the billions of dollars in development investment that Metrorail stations are attracting in the areas in most need of it. Further, city officials do not appear to take competition from the suburbs seriously enough.