I-95 south to the Beltway might be ok around rush hour but then it gets ugly..... I live in McLean. I assure you that the Beltway is bumper to bumper over the bridge from Maryland.

Once I got stuck on the beltway around 5 pm on a Friday when drove back from PA on I-270 against traffic, but then I got stuck for nearly 1 hour on a stretch that normall takes ~7 minutes. There was no accident or road work.

It might not seem logical since Tysons is an employment hub. If you travel from Tysons/McLean to Springfield during the AM then there is light traffic and vice verse in the PM. However, it appears to be really bad in either direction toward Maryland during rush hour.

In summary, I would avoid IAD. However, if you want to fly UA non-stop to S. America or Europe (FRA/LHR) then the ~21:30 flights might be possible. Then you can wait to drive south until 6:45 or and hope that you get there by 8 pm.

BWI also has the best domestic fares in the region due to Southwest. However, it's a rotten airport with bad parking system. They used to charge $30 for in-terminal parking whereas IAD/DCA charge $15. However, they have decent private parking companies like Airport Fast Park (or something like that). They are pretty efficient in getting you quickly to the terminal but I hate using a shuttle. Never use the airport run long-term parking options.