I would not know what to tell you about a trip like that. It seems like you might have to cross the Appalachians or Piedmonts unless you go south around the southern end.
Actually, you could follow the Atlantic route south to Jacksonville, Florida, and take highway 90 through to Austin. However, once you hit the border between Florida and Alabama, 90's surface and what side lanes still exist deteriorate quite a bit. Alabama, Mississippi, and Louisiana have very poor road surfaces compared to 90 in Florida. Sure, the road surfaces are improved here and there, but the picture is more what you might expect to encounter in developing and third-world countries. I think it has to do with the fact that that part of the country, mainly Louisiana, is a flood plain on top of 7000 feet of silt (New Orleans anyway). They have a gargantuan problem maintaining water levels, and controling the shifting of the mouth of the Mississippi river. The unstable, marshy, ground messes up their roads.
This message was edited by Westinghouse on 10-20-08 @ 4:30 PM