We've always found Fredricksburg, VA, just north of Richmond, to be a good mid-point. We would get in later at night, but sleep in a bit, grab breakfast by 9 am and hit DC well after the morning rush. We could also clear NYC before the afternoon rush. We never had luck with CT traffic which is the cork in the New England bottle. We would usually go as far up I-95 or the Merritt as we could before traffic came to a stop and have dinner at Friendly's (they are everywhere in CT) to get off the road for a few hours during the peak of rush hour. By the time we resumed travel, the roads were wide open and we'd be in central MA in about 2 hours more travel.