Urban sprawl is on the rise, but not in the Bay Area
As metropolitan areas expand rapidly to fit the world’s ever-growing population, a first-ever global study of street networks indicates that sprawling roads are on the rise, cementing a future in many places where relying on personal vehicles is the norm.
Streets crowded with carbon-spewing commuters are an obvious source of greenhouse gas emissions. But the layout of a community’s streets might be the driving force behind a person’s preferred transportation. Adam Millard-Ball, a co-author of the study published in January in Proceedings of the National Academy of Sciences, said that more connected streets provide better access to “greener” options for getting around, like public transportation, walking routes and bike paths.
But the cul de sacs, looping streets and dead-ends that are common in many suburbs and gated communities encourage driving. Millard-Ball, who is an environmental studies professor at UC Santa Cruz, said street disconnectedness is one indicator of sprawl. And the Bay Area, while having less sprawl than the U.S. average, is still a mixture of different road networks with varying levels of connectivity.
“Much of what has been built over the last 50 years has been in kind of sprawling style of development,” he said. But places like Redwood City and Palo Alto have maintained “much of their original character, even though they’ve been subsumed by urban growth.”
The researchers developed an index of sprawl by measuring the connectivity of all the world’s streets. An algorithm scanned an open-source online map system, identifying obstructions to pedestrian paths, like loops and deadends. With this data, the researchers assigned a score based on how disconnected an area’s streets were — the higher the number, the more sprawl — and mapped their results. The map is available at www.sprawlmap.org.
City centers, like downtown San Jose or San Francisco, are highly connected. Their grid networks often reflect their origin in an era before widespread vehicle use, when they were smaller, more walkable towns. As in many places around the world, most sprawl is due to rapidly expanding developments on the edge of dense cities.
If downtown grids are among the most connected network types, MillardBall said gated communities, which have few entry and exit points, represent the other extreme. People in these communities are more prone to driving, because the walled-off neighborhoods become a hindrance to accessing public services.
“You might live 20 feet from a bus stop, but it’s a 10-minute walk (to get there),” he said. “By design, it’s circuitous. It’s doing everything it can as a neighborhood to force you to drive.”