DC has a publication called "Transportation tips during an emergency incident."

It lists 19 "official" evacuation routes. IMO, even using all 19, it will at best very very slow. As Dagny points out there are other routes. IMO, trying to drive out will be impossible. Walk, cycle, scooters, dirt bikes and motorcycles will be the best alternatives.

link to the "tips:" http://ddot.dc.gov/sites/default/files/d...edness_2011.pdf