Evacuate, but not so far. That is what we do in Florida. All you need to do is get people back away from the storm surge, 5 miles or so.
Sorry, but the terrain around Houston is quite different. Even Dallas could have been flooded if Rita had gone straight for her. Dallas is protected by levees and the downtown is bowlshaped.
They need to go far enough, but when they do they might find themselves in a great, open, barren space with no resources at all except what they brought with them. That is what they should do, of course, bring tents and food, water for a few days. Not everybody needs to jump into cars and count on infrastructure existing out into the vast, empty plains.
In a direct hit, storm surge would have gone right up the Houston Ship Channel and flooded the city