Hit the slug line at Rolling Valley Mall - the absolute best, most efficient, and free way (if you're not driving) to get downtown. HOV 3 on 395 - from the time you get in a car, you can can be in DC in 20-25 min. You can occasionally run into some weirdos, but for the most part you see the same people every morning and evening and people look out for each other. Great system.
http://slug-lines.com/