Thinking about DC and the events that could trigger a mass evacuation, a big hurricane ain't it -- that might be a go home early or don't go to work event, but not a mass exodus. By the time it moves that far inland a Cat 5 will be a Cat 3, lotsa rain and flooding at lower levels with storm surge near river level, but nothing to trigger a mass move to W.VA.

A man-made event could trigger it, but for that there would be little to no warning and the goal would be to move upwind.

Dagny,
What specific events do you see triggering such an evacuation and how much forewarning do you expect? Congress and the W.H. will have the most warning and will be long gone before the word gets to the general population.

Don't know your living situation, but unless you live at the level of the Potomac, I'd prep to bug-in or to have some strategic withdrawal points around town that would be "upwind". If you do decide to leave pack quickly and leave. You really won't have time to coordinate with your neighbor, triage his stuff and pack. Just load your pre-packed stuff into the Element and Go.