Motor vehicles are a significant source of urban air pollution and are increasingly important contributors of carbon dioxide and other greenhouse gases. As awareness of the potential health effects of air pollutants has grown, many countries have implemented more stringent emissions controls and made steady progress in reducing the emissions from motor vehicles and improving air quality. However, the rapid growth of the world’s motor-vehicle fleet due to population growth and economic improvement, the expansion of metropolitan areas, and the increasing dependence on motor vehicles because of changes in land use has resulted in an increase in the fraction of the population living and working in close proximity to busy highways and roads — counteracting to some extent the expected benefits of pollution-control regulations and technologies. The Health Effects Institute (HEI) summarizes and synthesizes information linking emissions from, exposures to, and health effects of traffic sources. To read the full report, click here.