City structure, obesity, and environmental justice: an integrated analysis of physical and social barriers to walkable streets and park access.

Local parks and walkable neighborhoods are commonly cited as elements of the urban environment that promote physical activity and reduce obesity risk. When those vulnerable to obesity-related diseases live in neighborhoods without these qualities, it works against environmental justice goals that aim for a fair distribution of amenities. We use geographic information systems (GIS) to evaluate the relationship between the distribution of populations vulnerable to obesity and proximity to parks and walkable street networks in Phoenix, Arizona, USA. Though previous studies have used GIS to assess the distribution of access to opportunities for physical activity, none have analyzed access to both parks and walkable resources at once. Neither have they included data that reflects findings on a smaller scale indicating that perceptions of resource quality, safety, and cultural relevance also affect physical activity levels. We include these safety and quality factors in our study through statistical data on traffic fatalities, crime rates and park size. We find that, counter to predictions, subpopulations generally considered vulnerable to obesity (and environmental injustices more generally) are more likely to live in walkable neighborhoods and have better walking access to neighborhood parks than other groups in Phoenix. However, crime is highest in walkable neighborhoods with large Latino/a and African-American populations and parks are smaller in areas populated by Latino/as. Given the higher prevalence of obesity and related diseases in lower income and minority populations in Phoenix, the results suggest that benefits of built environments may be offset by social characteristics. Our most consistent finding indicates a strong negative relationship between the percentage of the population under 18 years of age living in an area and the likelihood that the structure of the built environment supports physical activity. Children under 18 are significantly underrepresented in regions deemed highly walkable and those with access to parks.