Wednesday, March 09, 2005

Sprawl in perspective

Just an interesting factoid: at our current average density of about 3,500 people per square mile (city limits), Houston's greater metro population of around 5 million would fit in a circle with a radius of 22 miles. Forecasts indicate we may add another 3 million people over the next 20-25 years, for a total of 8 million(!). Wanna take a quick guess what the radius of that circle would be?

A mere 27 miles. Just 5 extra miles. That's a single, solitary mile every 4-5 years. Not as many or as fast as you thought, huh? It's the power of the r-squared in the area=pi*r^2 equation. Of course, cities don't actually grow in a nice, uniform density - there are plenty of gaps and areas where the population stretches farther out (usually along freeways), plus the natural densification of the core. But the math shows how cities can seem to have galloping growth early on, as each mile of additional radius just holds a small number of people, yet that radial growth must inevitably slow as the additional miles can accommodate ever more people.

One implication: the Grand Parkway is likely to be the last loop we ever need.

4 Comments:

At 5:22 AM, March 22, 2005, Anonymous Chris Ruiz said...

In order for Houston to become a world class city, it is going to have to start fighting sprawl. Believe it or not, sprawl is a product of white flight, which leaves behind areas left to decay until someone decides to gentrify. Alief and Sharpstown are two great examples of what happens when everyone leaves the neighborhood. I believe that higher density developments that not only renew areas but add to the community could be used to discourage sprawl. Higher density developments can also be designed to be transit friendly, pedestrian friendly, and even bicyclist friendly; all three take cars off the road. Texas is losing more land to sprawl than any other state and Houston simply cannot continue spreading out forever. Air quality in Houston is already horrible. Without a change, things will only get worse for the quality of life in Houston.

 
At 2:19 PM, March 22, 2005, Blogger Tory Gattis said...

Ironically, the best way to fight sprawl and renew the core is by making aggressive mobility investments (including freeways) into the core. When you look at what happens to cities that don't do this (like LA, DC, Atlanta, Phoenix, Detroit), employers flee to the outer loop suburbs, allowing people to live even farther out. By keeping employers in the core, you naturally encourage core redevelopment and densification.

Although it seems like additional freeway capacity will cause people to live even farther out, the reverse is actually true: people generally want to be within 30 minutes of work, and even at 60mph that's no more than 30 miles out (and in reality, much less). Freeflow mobility => employers stay in the core => people stay within 20-30 miles => the core stays attractive and redevelops with higher densities (as is currently happening in Houston).

 
At 7:40 PM, April 01, 2005, Anonymous Murph said...

Just stumbled across this site. I have to offer a rebuttal to Tory - as an urban planning student at UMichigan, I can say for certain that "agressive mobility improvements into the core" would do nothing for Detroit if they were freeways. There's already plenty of freeway-mobility into and out of Detroit (one of Detroit's big problems right now is *local* accessibility - too many freeways cutting off neighborhood islands and stranding them with no easy access to destinations). If you build more freeways into Detroit, people will use them the same way they use the existing ones: hop on the freeway in one suburb, cut through the city, and continue on out the other side to a different suburb. If all you're providing is auto-mobility, you're not doing any favors from the core; you're just forcing all of the externalities of a freeway onto the community that contains them (Detroit) so that people can cross from suburb to suburb more easily.

Historically, it actually worked the other way around. Detroit's freeways enabled white flight (and general middle-class flight) by allowing people to move to the suburbs while still maintaining "reasonable" commutes to their jobs. Then the jobs followed out to the suburbs. The freeways pulled people out of Detroit - they're not a method for bringing them back in.

 
At 11:09 AM, April 02, 2005, Blogger Tory Gattis said...

Detroit strikes me as a warning for Houston that, once employers hit the tipping point and flee to the suburbs, getting them back is almost impossible. Even if Detroit somehow becomes new urbanist "creative class central", I think the employers are likely to stay where they are and just let those employees reverse commute.

Every year, employers in the core have to weigh up the pros and cons and decide whether to stay or move to the suburbs (commute times being just one of the variables). Their natural intertia is to of course stay, for simplicity and because their employees may be scattered all around the edge of the city - so moving to a particular edge suburb is going to really hurt the commute of many of them not near that particular edge.

But once commutes become so bad they can't stand it anymore (or, in the case of Detroit, if mobility was fine, maybe other factors made the core unattractive), they'll bite the bullet and move to a suburb. The employees will go through a painful transition process, many having to move to that suburb to keep a reasonable commute. But once they've gone through the pain of the switch and gotten all the employees near that suburb, I don't see any way you get them to go through that pain again to come back to the core, no matter how attractive it becomes. Do the companies of Silicon Valley want to move into San Francisco? Does Microsoft want to leave Redmond for Seattle? Are Orange County companies going to head for downtown LA? Not likely.

Mobility investments to the core help you keep the employers you have, not bring in new ones.

 

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