This indeed did happen last year the day before Charlie when the Tampa area was in its sights. The traffice was backed up from St. Pete through north Tampa all day and into the evening. In the middle of the night things calmed down considerably, and a guest we had from Virginia had a clear sail going home at 1:00 am.
Things in your area may be different, though, since it appears a lot more people are evacuating. Just trying to give you a word of encouragement :)
One thing that these traffic images illustrate is how woefully inadequate our road system is.