Introduction Most studies have shown that populations with lower socioeconomic status tend to experience higher levels of exposure to environmental air pollutants. We investigated the association between neighbourhood socioeconomic status and traffic related air pollution in São Paulo.

Methods We calculated total traffic density and traffic density for vehicles powered by gasoline and diesel, from traffic counts data, for 4964 geographical units with a population of 20 or more inhabitants, formed by a grid of 500 by 500 metres. The Human Development Index (HDI) was used as a socio-economic indicator and obtained for each of these geographic units. We analysed the association through logistic regression models for traffic density categories.

Results The neighbourhood socio-economic status was positively associated with all measures of traffic density with clear dose-response gradient. The category with the highest HDI presented Rate ratios of 10.2 (95% CI 7 to 14.9), 9.6 (95% CI 6.6 to 13.9) and 17.5 (95% CI 10.8 to 28.4), respectively, for total, gasoline and diesel vehicles traffic density.

Conclusion Our analysis suggests that richer areas are more exposed to traffic related air pollution. The greatest socioeconomic difference in exposure was found for diesel exhaust. In search of a more equitable solution of this environmental problem, investigations are warranted in megacities of developing countries about how the development of the road network and vehicle traffic relates to sites historically occupied by different social classes.