From Arlington, you're best off just catching I95, though as others have posted, it isn't a picnic on Friday/Saturday.
We sometimes head south toward DC (from PA) out Old US 15 down to Warrenton, and pick up Route 17 down to Fredericksburg. Not really an option for you. But it does eliminate the hassle that is the Capital Beltway. At Fredericksburg we endure I95 down to Richmond, and pick up I295. We stay on I295 almost to the end, and jump on Virginia Rt 460. That takes your through some nice scenic country - filled with many Barney Fifes and VA State Troopers mind you. But it is infinitely better than I64. It brings you out below the Monitor Merrimac Bridge Tunnel, and it is only a few miles to Rt 168 down to Rt 158.
This has served us well over the years.