Here's some advice ...
1. Start walking northwest up I-45. A normal person can walk 6mph. Rita is headed your way at 9mph, but you have a several hundred mile head start and Dallas is (only) 240 miles away.
2. Pack essentials in a backpack. 6000 calories of non-perishable food that can be eaten without cooking and 3 gallons of water.
3. As gay as it sounds, an umbrella will knock off some of the sun and make a decent impromptu club. Besides, it's going to rain wherever you go in the next day or two.
4. For protection, a knife if you're a guy, a palm pistol (ie. a Jennings .22) if you're a gal and a roll of quarters if you're a felon.
5. If you outwalk the traffic jams, cash money will be needed for bribing a motorist to drive you up the road a piece. BTW, you're looking to hitch a ride in a smaller vehicle with no more than 2 people inside. A van is a good place to be murdered.
6. When you get to safety, a credit card or two will get you a hotel room.
7. If you can't get a hotel room, try the corner booth of a 24 hour restaurant/diner and a thick book (ie Bible or Moby Dick). Be quiet. Order 1 item at a time and tip well. When the waitress starts pestering you, order 1 more item, tip well and be quiet. When the waitress gets irate with you, tell her to call the cops and be quiet. The cops won't give a flyin' rat's ass about a paying customer reading a thick book until Rita is long dead. (Ditching your knife or gun before you start loitering is a good idea.)
8. Relax. You're going to have a bad weekend. Everybody in Houston is going to have a bad weekend! Panicking or getting pissed off isn't going to change a thing.