“What is the influence of street network design on public health?” This question prompted a recent study that has just been published in the Journal of Transport & Health. While much has been said about the impact of various aspects of the built environment on obesity levels, heart disease, cancer rates and so forth, this study particularly focused on street layouts: comparing the health of residents of car-friendly cul-de-sacs with residents of walkable, densely networked inner cities. So, which of these makes you more sick?
The study was performed by Wesley Marshall, Daniel Piatkowski and Norman Garrick from the University of Colorado Denver, Savannah State University and the University of Connecticut respectively. The study examined 24 Californian cities “exhibiting a range a street network typologies” and compared them using data from the California Health Interview Survey. According to the study’s abstract: “The three fundamental elements of street networks are: street network density, connectivity, and configuration.”
In practice this meant that the study compared levels of obesity, diabetes, high blood pressure, heart disease, and asthma between high-density, inner-city neighborhoods with high walkability and increasingly sprawling, “tree-like” neighborhoods where urban design requires residents to drive everywhere. A previous study by Marshall and Garrick had found that residents of neighborhoods built on a hierarchical, tree-like system of roads spent on average 18 percent more time commuting than those who lived in grid-based cities.
After implementing controls for “the food environment, land uses, commuting time, socioeconomic status, and street design,” the results showed that increased intersection density was significantly linked to a reduction in obesity at the neighborhood level and to reductions in the rates of obesity, diabetes, high blood pressure, and heart disease at the city level. “The more intersections, the lower the disease rates.” The study also found a correlation between wider, multi-lane roads and higher rates of obesity and diabetes. The authors surmised that multi-lane roads indicated a less pedestrian-friendly environment. Big box stores also indicated reduced neighborhood walkability and their presence was “associated with a 13.7 percent rise in obesity rates and a 24.9 percent increase in diabetes rates.”
However, as Marshall told James Hamblin of The Atlantic, “It’s nice to make more of these connections, but it’s hard to say that these kinds of neighborhoods [walkable inner cities] cause good health.” The study raises questions such as whether people who prefer to walk for the sake of their well-being choose to live in a more walkable environment in the first place and therefore their urban environment simply supports their pre-existing health and fitness goals. The authors admit that “Given the cross-sectional nature of our study, proving causation is not feasible but should be examined in future research.” However, they also note, “It might not be common for people to explicitly contemplate health when selecting a place to live, but this research indicates it is worth considering.”