Bumping this up so someone from DC will see and post.
I-95 and I-495 make up the beltway. IIRC, the bulk of the current roadwork is on the portion of the beltway from the Springfield interchange (or the "mixing bowl") where I-95, I-495, and I-395 all meet through the Wilson Bridge. Think of the beltway like a clock -- the Springfield Interchange is at 6 and the Wilson Bridge is counterclockwise from there around 5. Coming south on I-95 you will hit the beltway around 1 or 2. Hopefully someone from DC can post the current conditions and progress.
An alternate is to take US 301 from Baltimore across the Nice Bridge ($3 toll IIRC) into VA and meet up with I-95 between Fredericksburg and Richmond.