Traffic Density and Mortality Risk in the 1991 Canadian Census Health and Environment Cohort (CanCHEC)

Abstract

Background: There is evidence that local traffic density and living near major roads can adversely affect health outcomes. We aimed to assess the relationship between local road length, proximity to primary highways, and cause-specific mortality in the 1991 Canadian Census Health and Environment Cohort (CanCHEC).Methods: In this long-term study of 2.6 million people, based on completion of the long-form Census in 1991 and followed up until 2011, we used annual residential addresses to determine the total length of local roads within 200 m of centroid of postal codes, and the subject’s distance to primary highways. The association between exposure to traffic and cause-specific mortality was estimated using Cox proportional hazards models, adjusting for individual covariates and contextual factors, including census division-level proportion in high school, the percentage of recent immigrants, and neighborhood income. We performed sensitivity analyses, including adjustment for exposure to PM2.5, restricted to subjects in core urban areas, and spatial variation by climatic zone.Results The hazard ratio (HR) for all non-accidental mortality associated with an interquartile increase in length of local roads was 1.05 (95% CI 1.04, 1.05); and for an interquartile range increase in proximity to primary highways, 1.03 (95% CI 1.02, 1.04). However, HRs by traffic quartile increased with increasing lengths of local roads, or closer proximity to primary highways, for all mortality causes. The associations were stronger in subject residing in urban core areas, attenuated by adjustment for PM2.5, and HRs showed limited spatial variation by climatic zone.Conclusion: In the CanCHEC cohort, exposure to greater road density and proximity to major traffic roads were associated with increased mortality risk from cerebrovascular and cardiovascular disease, ischemic heart disease, COPD, respiratory disease, lung cancer, and with unclear results for diabetes.