While it lacks many types of zoning, Houston still has minimum parking requirements, which push people towards driving. It also exists in a conservative state that favors highway expansion over transit expansion.

An interesting view of how parking affects Houston is at http://www.citymetric.com/transport/what-bombs-did-rotterdam...

The great thing about Houston from a market urbanist perspective isn't that it's particularly dense or walkable, but that it's dirt cheap for the amenities it does offer.