We did a DC-Florida road trip last year during that time, stopping in SC for a night. We drove from DC to SC on Christmas Day and of course there wasn't any traffic. I would guess that the day after Christmas is probably not too bad either (we drove from SC to Florida that day and didn't hit major traffic). I do think you're likely to hit a lot more traffic on the trip home. On our return trip last year we ended up stopping for a sitdown dinner around Richmond, I think, to wait out the typical Fredericksburg area backup.