A friend of mine lives just South of Houston and tried to evacuate. After about 6 hours on the road they had only made it 20 miles North. They gave up and headed back home to ride it out rather then being stranded on the highway.
I think they have learned how to help people evacuate. Have gasoline available at different intervals on the highways for people who run out of fuel. Same with bathroom stops - portables. Some snacks or easy to eat food to help with the little kiddies have no idea its hot, nothing is on at home, everybody is driving, AND WHERE ARE WE GOING? I also think they are going to reinforce when people should leave by their zip code zones. If you in direct path and are in the zip, you go first. As zones are cleared, more zones are let to go for evacuation.
I think these few things will really help to help people evacuate in the future - should help freeways (are backroads!) to clear more easily.
But, every storm is different. There are always unintended events.