Trains would have been the best bet if they had started early enough, but by the time they got around to doing something, it was probably too late. The line that runs north runs right along the shore of the lake (Inches from the water and inches above the water). The line west crosses the Huey Long bridge (scary to drive across even in good weather) and then goes across low country on the west bank. The line east goes across the outlet from the Lake, and would just put folks in the path of the storms hitting the Mississippi coast.
Perhaps we'll see more development of the rail system as an aftermath of this - rail is *still* the most efficient ground transport system for evacuation and linear transport.