How far does a city sprawl? I tend to measure it based on the last planned community of at least a couple hundred acres. Of course there will always be small plats of estate residential, single cul-de-sacs and so forth, but if you class that development as “urban sprawl” then 75% of Pennsylvania is urban. Which is, obviously, not true.
So how far out does a city like Houston go? Head out on IH 10 and in 30 miles you’re through the Energy Corridor, past Katy Mills and into the prairies. Eastbound, the same 30 miles puts you past Baytown and into the swamps. Head southwest on 59 and it’ll take you 37 before you’re through Rosenberg and wondering why the speed limit hasn’t jumped to 75 yet. Via 288 it’s a scant 23 miles. Towards Dayton it’s 25, towards Kingwood it’s 32, towards Brenham it’s 35, and towards The Woodlands it’s a tough 42 mile slog as the Houston metro blurs into Conroe.
What about Phoenix?
Heading west on IH 10, I’d call the “end of sprawl” at Arizona 85, which is 40 miles. Eastbound (geographic south) you can get out in 24. Stay on the Superstition Freeway and it’s 34 miles to the turnoff for Gold Canyon. Running northbound on I-17, it’s 34 miles to get through Anthem. And while a straight shot out Highway 60 will get you through Sun City in only 28 miles, in practice it’ll seem like a lot longer when you’re waiting for the traffic lights. Take 10 to the Agua Fria and it becomes 35.
What you can gather, then, is that Houston and Phoenix cover essentially the same geographic area. But where Phoenix has 1.5 million people in a metro area of 4.3 million, Houston holds over 2 million in a metro of over 6 million, and that’s not including Galveston.
How does H-town pack 33% more people into the same basic geography? Zoning. Or the lack thereof.
Phoenix is mostly zoned under traditional postwar Euclidean codes. Minimum lot sizes are stipulated. Apartment complex density is regulated, and apartments are banned outright in many areas. Commercial and industrial zones have fractional FARs which ensure that a majority of the land will always exist as surface parking lots.
Houston has… nothing. In the past, there was a 5,000 square foot lot minimum for single-family dwellings, but it never applied to condos or townhomes, it was subsantially less than many of Phoenix’s single-family districts, and in any event it’s much smaller now, only 1400 square feet in places. Apartment developers are free to pack as many units into a site as they can, and do. And while commerce is subject to minimum parking requirements, builders are free to satisfy those however they want. Which is how you get things like this ridiculously labyrinthine parking garage. This sort of simple lot maximization in a suburban context isn’t possible under most height or FAR requirements, and is something you don’t often see outside of the Houston metro.