Not sure yet. Somone recommended the "Skyline Drive" south from Front Royal which I see from my map is actually in Virginia. Grateful for any suggestions.
Although Skyline Drive is very pretty, it is a VERY long drive from DC. Dubious that you can make it there and back again in a day, especially once the leaf-peeping has begun, as traffic on Skyline Drive slows to about 25 mph. Easier to do in a day would be drive out to western Maryland, toward Deep Creek Lake. The entire jaunt is on limited access interstate highways, and you will see some pretty spectacular landscape on the way. If you're so inclined, you can take a reasonable side-trip off the freeway and go visit Fallingwater and Kentuck Knob, two Frank Lloyd Wright houses, if you're architecturally inclined. Check with the Fallingwater website for booking your ticket - they may still require them in advance at this time of the year.