Previously rural counties like Calvert in Maryland and Loudon in Virginia have a habit of enacting strict slow-growth policies, limiting the number of residential developments that can be built.
Sadly, Washington has a habit of attracting people to come here to work, and is one of the few places in the country where unemployment is relatively low. As more people come to live here... they have no place to live, because all these suburban counties won't let them build homes. So property values go up because the supply of homes is low. And thus, people move even further and further out in an attempt to find affordable housing, thus clogging the roads of the slow-growth counties anyway.
The only way to limit growth is to stop being so attractive to potential workers. Fewer new jobs would mean fewer new residents and slower growth. But since everybody wants more new jobs in order to spur on the economy, population growth is going to continue whether these outlying counties want it or not.