I ride after work by bringing my bike to the office in my car. (Sorry guys, I just don't want to commute by bike...) There's a trail across from my office but it's very crowded, so I usually only use it for a couple of miles to get to some quiet neighborhoods. By borrowing cue sheets from a local club and modifying them to minimize high-traffic roads, I can ride for > 20 miles with few problems. And I focus on hills to make the most of a shorter workout.

You might want to look into the Baltimore Bike Club -- they might have some rides that aren't too far from where you live. Also try http://www.bikewashington.org. They have a yahoo group; I haven't been on it in a while but there might be folks there who know your area and can suggest good cycling routes.