Traffic emissions are the major source of air pollution in urban centers, and concentrations of traffic pollutants are higher near busy roads. We conducted a cross-sectional study of children (n=1080) living at varying distances from high-traffic roads in the San Francisco Bay Area, a highly urbanized region in Alameda County characterized by good regional air quality due to coastal breezes. Health information and home environmental factors were obtained by parental questionnaire. This current study builds on an earlier study of this population where children’s pollutant exposures were based on measurements taken at neighborhood schools. In the earlier study, we found modest associations between traffic pollutants and current asthma and bronchitis based on a two-staged analysis. In this project, exposure estimates were developed for smaller spatial scales using geographic information systems (GIS) methods and utilized in health analyses. Associations with respiratory morbidity were examined using several measures of residential proximity to traffic calculated using GIS including: (1) traffic metrics that measure traffic distance, volume and/or density; and (2) a land use regression model (LUR) that predicts nitrogen dioxide (NO2) for Alameda County. We found that various efforts to enhance estimates of traffic exposure resulted in stronger associations with respiratory morbidity, particularly current asthma symptoms. For example, stronger associations were found when we restricted the sample to those living close to the school-based measurements. Traffic-based estimates developed through GIS were moderately correlated with actual pollutant measurements, especially nitrogen oxides (NOx) and nitric oxide (NO), and also associated with current asthma.
The highest risks of asthma were among those living within 75 m of a freeway/highway and those exposed to very high levels of nearby traffic density. A land use model developed for Alameda County successfully predicted NO2 concentrations which were then found to be associated with current asthma. There was poor agreement between self-reported residential proximity to traffic and more objective measures using GIS methods. Our findings provide evidence that even in an area with good regional air quality, proximity to traffic is associated with adverse respiratory health effects in children.