Structural Disparities of Urban Traffic in Southern California: Implications for Vehicle-related Air Pollution Exposure in Minority and High-poverty Neighborhoods

Structural inequalities provide an important context for understanding and responding to the impact of high traffic densities on disadvantaged neighborhoods. Emerging atmospheric science and epidemiological research indicates hazardous vehicle-related pollutants (e.g., diesel exhaust) are highly concentrated near major roadways, and the prevalence of respiratory ailments and mortality are heightened in these high-traffic corridors. This article builds on recent findings that low-income and minority children in California disproportionately reside in high-traffic areas by demonstrating how the urban structure provides a critical framework for evaluating the causes, characteristics, and magnitude of traffic, particularly for disadvantaged neighborhoods. We find minority and high-poverty neighborhoods bear over two times the level of traffic density compared to the rest of the Southern California region, which may associate them with a higher risk of exposure to vehicle-related pollutants. Furthermore, these areas have older and more multifamily housing, which is associated with higher rates of indoor exposure to outdoor pollutants, including intrusion of motor vehicle exhaust. We discuss the implications of these patterns on future planning and policy strategies for mitigating the serious health consequences of exposure to vehicle-related air pollutants. Travel provides an essential link between people and social, economic, and recreational activities in metropolitan areas. Despite these benefits to regional prosperity, vehicle travel is increasingly responsible for numerous externalities including heightened congestion, increased noise, and diminished air quality due to vehicle-related pollutants. The distribution of these externalities within the urban environment is deeply embedded within *Direct Correspondence to: Douglas Houston, The Ralph and Goldy Lewis Center for Regional Policy Studies, School of Public Policy and Social Research, University of California, 3250 Public Policy Building, Los Angeles, California, CA 90095-1656. E-mail: [email protected] JOURNAL OF URBAN AFFAIRS, Volume 26, Number 5, pages 565–592. Copyright # 2004 Urban Affairs Association All rights of reproduction in any form reserved. ISSN: 0735-2166. the urban structure and related to persistent inequalities such as racial segregation, concentrated poverty, and uneven land use development. This article documents ways that historic and structural patterns within Southern California provide an important context for understanding the causes, characteristics, and magnitude of traffic, particularly for disadvantaged neighborhoods. We’ve just begun to understand the health costs of heightened levels of vehicle-related pollutants immediately adjacent to heavily traveled roadways and know little about the demographic and socioeconomic groups exposed to these pollutants. Documenting and quantifying the distribution of traffic density in Southern California is an essential step and prerequisite to understanding potential exposure patterns and in formulating policy and planning interventions that can help minimize the hazardous impact of vehicle-related pollutants. We begin by discussing the adverse health effects of traffic-related pollutants and current regulatory approaches to improve regional air quality. We then describe the growing evidence that these pollutants and related health impacts are concentrated within hundreds of meters of major roadways. This raises a number of distributional concerns, especially given the uneven distribution of environmental hazards in Southern California. We provide a framework for understanding environmental disparities in the region by identifying geographic patterns of racial segregation and concentrated poverty in Southern California and by documenting the overlap of disadvantaged neighborhoods with regional job centers and the transportation network. We present our finding that minority and high-poverty neighborhoods in the region bear over two times the level of traffic density compared to the rest of the region. We conclude with a discussion of the implications of our findings for environmental justice research and strategies for mitigating the localized impacts of vehicle-related pollutants. ADVERSE HEALTH EFFECTS OF VEHICLE-RELATED AIR POLLUTION Vehicle traffic remains a major and often dominant source of air pollution. In Southern California, on-road mobile source emissions are responsible for about 76% of carbon monoxide (CO), as well as 45% of volatile organic compounds (VOC), and 63% of nitrogen oxides (NOx), the precursors to ozone and other components of photochemical smog (South Coast Air Quality Management District, 2003). The geographic dispersion of these and other vehicle-related pollutants within the region varies based on a number of factors. The concentrations of primary pollutants that are directly emitted into the air are typically highest close to their sources. Secondary pollutants such as ozone are gases or particles not directly emitted into the atmosphere that form in the atmosphere because of chemical reactions of precursor compounds, often driven by sunlight. They tend to reach their highest concentrations some distance downwind from the original emission source. The prevailing daytime sea breeze in Southern California tends to transport pollutants from coastal areas to the inland valleys where secondary pollutants reach their maximum concentration. A vast body of scientific evidence has documented the adverse health effects of vehiclerelated pollutants including chronic illness, lung impairment, and increased morbidity and mortality (Table 1) (American Lung Association, 2002; Hall, Winer, Kleinman, Lurmann, Brajer, & Colome, 1992; South Coast Air Quality Management District, 2003). These adverse health effects have a serious impact on California’s economy. In 1998, hospitalization and medication costs for asthma in the state totaled $1.3 billion (Asthma and Allergy Foundation of America, 1998). Exposure to air pollution in the state is responsible for about 2.8 million lost workdays each year and over $3.5 billion in hospitalizations and 566 | JOURNAL OF URBAN AFFAIRS | Vol. 26/No. 5/2004