If you're running 81N to 95N, or 95S to 81S, here's a nice little shortie I use to get aroud DC...
Take 7 east (south) to US340 east (north) to Frederick, MD, and jump on 70E there. Smooth ride, few lights, and 4 lanes except in WV. At night there's very little traffic.
Beats taking 81 all the way to 70; or 66 across.