Living near traffic has been associated with asthma and other respiratory symptoms. Most studies, however, have been conducted in areas with high background levels of ambient air pollution, which makes it difficult to isolate the independent effect of traffic. Additionally, most investigations have used surrogates of exposure, and few have measured traffic pollutants directly as part of the study. In http://www.ehponline.org/members/2008/10735/10735.html, researchers conducted a study in the San Francisco Bay Area and obtained health information and home environmental factors by parental questionnaire; the use of questionnaires, as opposed to direct observation and measurement, has previously been noted as a weakness in many studies. The researchers assessed exposure to air pollution with several measures of residential proximity to traffic calculated using geographic information systems, including traffic within a given radius and distance to major roads; they also measured traffic-related pollutants (nitrogen oxides and nitrogen dioxide) for a subset of households to determine how well traffic metrics correlated with measured traffic pollutants. Using statistical regression analysis, the researchers found an association between the existence of current childhood asthma and proximity to traffic. Children whose residences were in the highest quintile of exposure had approximately twice the adjusted odds of current asthma (i.e., asthma episode in the preceeding 12 months) compared with children whose residences were within the lowest quintile. The highest risks were among those living within 75 meters of a freeway or highway. Most traffic metrics correlated moderately well with actual pollutant measurements. The researchers reached the following conclusions: "This study adds to a growing body of evidence linking proximity to traffic and adverse respiratory effects. When we initiated this study, several studies, primarily in Europe, had identified associations between proximity to traffic and adverse respiratory outcomes. However, extrapolations of the results of European studies to the United States is subject to a variety of sources of uncertainty, including differences in fleet composition (diesel vs. gasoline), emission controls, land use patterns, and population characteristics. Additionally, California has the most stringent emissions standards for motor vehicles in the United States. These differences could result in lower exposures to traffic pollutants among California residents relative to those in European cities.
Our study location and design allowed us to evaluate the effects of traffic pollution in a region of California with relatively low levels of regional air pollution. This restricted study area allowed us to focus on variations in air quality related to localized traffic-related air pollution. Our air monitoring pilot study confirmed that this small area variation in air quality was attributable to local impacts of traffic. Therefore, our study implicates local traffic as an important risk factor for respiratory disease in an urban area that meets federal air quality standards for ozone and annual average PM2.5 and has rare exceedances of the 24-hr PM2.5 standard. Other American studies of traffic and respiratory health involving populations from Southern California, the northeastern United States, and Anchorage, Alaska, had moderate to high regional levels of ozone and/or PM2.5 or volatile organics from gasoline exhaust. Thus, our study provides additional evidence that local traffic may have respiratory impacts even in an area with good regional air quality." [References to published papers omitted; see article for cross-references.] As noted in several prior posts at http://eartotheground.typepad.com/, living near traffic has been associated with asthma and other respiratory symptoms.