I know, I know. I used to live there. If you "go with the flow" you will end up going about 10-15 mph above the speed limit. I've driven in bumper-to-bumper traffic. I've driven in extremely fast traffic. But only on I-95 and I-495 have I driven in extremely fast bumper-to-bumper traffic inches (literally!) from each other at 80 (or more) mph.
At least the threshold is relatively high for now, I suppose. Going with the flow on 66, when we're all moving nicely, usually means about 70-75 in a 55. Still, as soon as legislators start feeling like they're digging for nickels in the couch cushions, look for it to be lowered, and then they can catch everyone.
Everytime we have gone there recently, we have been lucky to be able to drive 10mph. Talk about frustrating! I hate to drive anywhere near DC. Either the traffic is bumper to bumper due to someone smashing another driver like a bug, OR they are doing some road construction and have shut down six lanes and left one open. OR both, leaving no lanes for driving 5mph.