13 January 2010

The Health Effects Institute (HEI) published today a new report, titled “Traffic-Related Air Pollution: A Critical Review of the Literature on Emissions, Exposure, and Health Effects”. The report—one of the most comprehensive and systematic reviews of the worldwide traffic emissions and health science to date—has found that there are substantial gaps in what we know about exposure to traffic air pollutants and their health effects.

Based on a systematic review and analysis of over 700 worldwide studies, the report found that the body of medical research provides little firm evidence on the relationship between exposure to traffic and disease. Sufficient evidence was found that exposures to traffic-related air pollution cause asthma exacerbation in children. While “suggestive evidence” also links traffic-related pollution to a number of other health effects, the existing data was deemed insufficient to establish a causal relationship.

While difficult to quantify, the health effects of traffic-related air pollution appear to be most severe along highways. The report noted that the zones most impacted by traffic pollution are up to 300 to 500 meters from highways and other major roads.

The report was authored by an HEI Special Panel, chaired by Dr. Ira Tager of The University of California Berkeley School of Public Health. The Panel, which included a dozen US and international experts in emissions, exposure, epidemiology, statistics, and public health, concluded:

  • Many countries have implemented more stringent vehicle emission controls and made progress in improving air quality. However, the rapid growth of the world’s motor vehicle fleet, the expansion of metropolitan areas, and the increasing dependence on motor vehicles have resulted in an increase in the fraction of the population living and working in close proximity to busy roads—counteracting to some extent the benefits of pollution control regulations.
  • Based on a synthesis of the best available evidence, the Panel identified an exposure zone within a range of up to 300 to 500 meters from a highway or a major road as the area most highly affected by traffic emissions and estimated that 30% to 45% of people living in large North American cities live within such zones.
  • Many aspects of the epidemiologic and toxicologic evidence relating adverse human health effects to exposure to primary traffic-generated air pollution remain incomplete. However, using rigorous criteria to assess cause and effect, the Panel concluded that the evidence is sufficient to support a causal relationship between exposure to traffic-related air pollution and exacerbation of asthma among children.
  • The Panel also found suggestive evidence of a causal relationship with onset of childhood asthma, non-asthma respiratory symptoms, impaired lung function, total and cardiovascular mortality, and cardiovascular morbidity, although the data were not sufficient to support causality. For a number of other health outcomes, there was limited evidence of associations, although the data were either inadequate or insufficient to draw firmer conclusions.
  • In the context of the continuing progress to reduce emissions from motor vehicles, the Panel noted that, since the epidemiology studies are based on past estimates of exposure from older vehicles, they may not provide an accurate guide to estimating health associations in the future.
  • In light of the large number of people residing within 300 to 500 meters of major roads, the Panel concluded that the sufficient and suggestive evidence for these health outcomes indicates that exposures to traffic-related pollution are likely to be of public health concern and deserve public attention.

The report also identified a number of top priority research needs to fill key gaps in our understanding of emissions, exposure, and health.

The Boston, MA-based Health Effects Institute is an independent, non-profit research organization funded jointly by the US government and the industry to provide high-quality, impartial science on the health effects of air pollution.

Source: Health Effects Institute