I usually take the side-path on Gallows when leaving Tysons toward Oak St, because I don't want to have to cross Gallows twice. On the way in towards Tysons I'll usually ride in the roadway.

Another way in that avoids Gallows is to exit the trail in Vienna by the old white railroad whatever-it-was just behind the Navy Fed. Credit Union. There's a very short gravel trail that takes you over to Electric Ave. It's rideable on a road bike. You can then take Woodford to Old Courthouse and go through various streets or parking lots to get to Rt 7.