Rob Goodspeed has a post on how smart growth policies in places like Montgomery County cause new development to leapfrog into more distant locales, including the panhandle of West Virginia. There are actually two centrifugal forces at work here: closer counties stepping on the brakes push growth out, while lax rules in outer counties (designed to attract some of the economic energy of the metropolis) pull growth out. The latter force means that even if you can convince inner areas to get bigger and denser, there will still be other places trying to bring sprawl to them, and once population is in outlying areas, jobs and calls for additional roads will follow.

This is why I emphasize regional rail as a solution to extreme sprawl. States should agree to build quality rail lines from distant towns into metro areas, as long as those towns agree to focus development around stations. The idea being that far flung areas get an economic boost without ruining the rural amenities that make them attractive in the first place, while state governments control their expenditures by paying for rail and limiting future highway plans (and defusing the urban-rural antagonism that’s common in so many parts of the country).

In this particular case, you could improve the feeder lines from places like Winchester and Martinsburg that run into the Germantown line to Union Station (which should also be upgraded to accomodate more trains at faster speeds). You could also run a new line from Charles Town through Leesburg to Dulles, where passengers could then pick up the Metro. Alternatively, see this (from Richard Layman).