While those plans are inadequate, for an area like DC, it would be difficult even to devise a unified, large scale evacuation plan, not to mention implement such a task. Others may have different opinions, but I don't think the DC metro area really needs a single unified evacuation plan, but rather, an increase of awareness, preparation and planning at the neighborhood level. Many businesses, hospitals, and universities already have their own plans in case of emergencies and evacuation routes, and residents who work or go to these places are covered, but a level of redundancy that covers residential areas would be essential to help everyone. The only need for uniformity would be to ensure that evacuation plans don't over tax local evacuation routes (even though thats going to happen anyways).
Some local areas are doing well as far as preparedness is going. PG county has a really robust disaster preparedness and relief system including a large and well organized CERT program, search and rescue teams (urban, suburban, and wilderness), faith-based disaster relief groups, and a county government that is willing to talk and work with all of them. I think they've actually go their heads on straight when they say to stay off the roads. Besides a wide spread nuclear attack, and one or two other events, I don't see any other emergency scenarios that would be made better by having everyone jump on a road and run.
The majority of the evacuation routes are already running at over capacity on a daily basis during rush hour (route 1, Georgia ave, any of the bridges crossing the Potomac, etc). Being stuck on these roads during any sort of disaster isn't going to help anyone's situation.
My personal plan is to bug in. My stockpile is still inadequate, but I'm slowly working it up to a respectable level, and in my judgment, will give me a better chance than either loading up my car and getting stuck on the road, or hauling my supplies out and walking to somewhere else. In the first case, I am putting my life in the hands of the metropolitan DC road system (which has already been thoroughly disparaged here), and in the second case, I would be able to travel 20 miles a day at the most, and most of the time I would be following the same road system that I would be driving on. Your mileage will undoubtedly vary, but bugging in will give me more protection against the most likely disasters, besides nuclear attack. In the case of such an attack and in case I was forewarned, my plan would probably be to grab my go bag (or anything) and try to use local roads that may not be as packed as main arteries will be (but probably still congested) and hope for the best. In the case of zombies, I would still prefer bugging in. I have a better chance of defending myself, or better yet, not being detected in my house than stuck on the highway.
All of that being said, the biggest problem facing us in the DC area will probably be the government response, especially if any sort of martial law is set in place by the military presence that will most likely appear after an event in DC. The things to do here would be to lay low, be non-aggressive, and keep the lines of communication open. The last thing you want after surviving a zombie attack is to get killed by the National guard because of an argument or misunderstanding. DC will be given much more attention and support during a disaster. A good portion of those resources will be allocated to heads of state and politicians, but this will most likely mean more resources for the residents as well. Politicians that abandon their constituents, or anybody, will be looked on very negatively, and the machine that runs the nation will most likely want to get back into working order as soon as possible. The Washington DC area does have the misfortune of being a high risk area as well having an inadequate evacuation/transportation system, but there will be some benefits to being closeby if the SHTF.
I survived NNY08WCT! We Bug Out Harder!