Leaving most large highly populated areas is an event, bugging out from said large highly populated area during a terrorist/weather/EOTW event is something you either do ahead of the event or you roll to Plan B -- Bugging In. For me, Plan B is the norm; unless I know to leave before the event the road East will be packed and one tank of gas won't get there. Forget North/South, that's LA or Mexico. West is wet.

Go early or don't go.

YMMV