Dagny, you raise an issue interesting to me, I was just reading a report of a 5 state disaster scenario in which local DC residents were polled and asked about their preparations in the event of an attack, it was a dirty bomb scenario - locally destructive, but not so heavy in terms of loss of life, but also likely to prompt many to evacuate large areas of the DC region. I thought it was interesting that the overwhelming majority in Virginian and DC/Maryland would plan to evacuate north and south, with only a small number heading west, to Pennsylvania and West Virginia, and the mountains. Report at http://www.vdem.state.va.us/library/behavior_study/index.cfm if you're interested.

This may just come down to local topography and available routes, but it strikes me that either you would head for the west because of where you live in relation to DC, or maybe because you are already familiar with the terrain, and you are truly prepared to head for a lesser populated region, which can support you in the event of a crisis?