This trajectory has had a lot of interesting consequences, which have been studied over the last several years by Norman Garrick at the University of Connecticut and Wesley Marshall at the University of Colorado, Denver. They've found that the kinds of communities illustrated at right tend to yield more fatal traffic crashes than the ones at left (perhaps because it's easier for cars in the former to pick up speed). People who live in the communities at right do more driving (likely because their destinations aren't reachable by foot or tend to be farther away). The kinds of places at left, meanwhile, have been linked to higher rates of biking and walking, which suggests they may in some ways also be healthier for residents.
Marshall and Garrick's latest research, published with Dan Piatkowski in the Journal of Transport & Health, adds to this last idea: They've now found that more compact and connected cities of the kind shown at left — which have a lot more intersections per square mile — are strongly correlated with reduced rates of obesity, diabetes, high blood pressure and heart disease.
The suggestion supports an idea of growing interest to public health researchers: What if the characteristics of where we live influence how healthy we are? This is more clearly evident when we think about factors like pollution and which places are exposed to more of it than others (other studies have investigated, for example, whether people who live near highways are more likely to have asthma). But it's another step all together to suggest that the way we plan communities — along old-fashioned street grids or meandering subdivisions — might have health consequences, as well.
Urban planning and public health actually have a long history together dating to the 1850s, when a British doctor named John Snow first mapped an outbreak of cholera in London to pinpoint its source at a public water pump. Since then, we've understood that the design of cities is related to sanitation and the spread of diseases.
Marshall, Garrick and Piatkowski, though, are talking about a different set of health concerns: not communicable diseases like cholera, but lifestyle diseases like diabetes. "The literature suggests," they write, "that the shift in industrialized nations toward a more sedentary lifestyle is linked to increasingly auto-dependent lifestyles, which in turn is linked to lower density developments and auto-friendly land uses." Maybe we're designing places, in other words, that make it harder to be active.
Their study looked at 24 medium-sized cities in California, built at different times and with a variety of different street designs. They then examined self-reported health data from the California Health Interview Survey, which sampled 40,000 to 50,000 adults in 2003, 2005, 2007 and 2009. Their analysis controlled for socioeconomic status, commute times, the presence of fast-food restaurants and grocery stores and other land uses. Ultimately, they found that higher intersection densities were significantly linked to reduced rates of obesity at the neighborhood level, and reduced obesity, diabetes, high blood pressure and heart disease at the city level.
They can't rule out the possibility that healthier people are simply self-selecting for these places. So this study isn't definitive proof that the kind of compact street designs conducive to walking and biking make people healthier. But it's a reasonable theory that if you live in a community where it's easy to walk to work and the grocery store or even just to the Metro (think DuPont Circle in Washington), then that physical activity woven throughout your life might accumulate over time into health benefits. Conversely, if you have to drive to all those places, and if those places are farther from you (think much of Northern Virginia), then you may miss out on the exercise of simply getting around.