When comparing the mean commuting times among America's large metro areas, something funny appears. "Although population is strongly correlated with commuting time, particularly when all metro areas over population one million are included in the sample, the differences are surprisingly small," notes Gardner. For example, "Orlando, with an urbanized area of only 600 square miles, has a mean commute just twelve seconds shorter than Dallas, which covers 1,780 square miles, although both cities have comparable densities, employment centralization and highway miles per capita."
So is there an inherent limit to the potential extent to which development will sprawl into the fringes of a metropolitan area based on a maximum mean commute time of around 30 minutes? Gardner seems to think so and describes how development in, and around Houston, might be shaped by such forces.
"This theory doesn't imply that outwards expansion will come to a screeching halt once some magical distance from the center is reached," writes Gardner, "but that the balance of new construction will attempt to shift to the core as commutes from fringe areas begin to significantly exceed 30 minutes."
Thanks to Daniel Lippman