Exposure to traffic has been associated with a number of adverse respiratory health outcomes including asthma symptoms.1 More recently, following mounting evidence that exposure to air pollution is linked to not just respiratory disease but cardiovascular disease as well, there has been interest in also investigating the effects of traffic exposure on cardiovascular disease.2

It is difficult to investigate traffic effects, particularly traffic pollution effects as distinct from effects of other traffic-associated exposures such as noise, for example. While traffic is a source of a large number of air pollutants, there is currently no air pollutant or pollution component that serves as a specific measure of traffic pollution. Ambient air concentrations of pollutants such as nitrogen dioxide and carbon monoxide are often used to reflect traffic pollution, but there are other sources of these pollutants. Concentration of particulate matter elemental carbon is often used to reflect diesel vehicle emissions specifically, but in many settings a substantial fraction of ambient elemental carbon is attributable to non-diesel emissions.3

For investigating long-term exposure effects of traffic exposure, an alternative to estimating exposure based on pollutant air concentrations has been to employ measures of traffic at relatively small spatial scales of tens of metres. Examples include proximity to large roadways, amount of traffic volume within a defined distance and traffic emission concentrations based on dispersion models.2 4 Tonne et al initially reported findings in which long-term exposure to traffic in …