How wide should be the adjacent area to an urban motorway to prevent potential health impacts from traffic emissions?

In recent years, several studies show that people who live, work or attend school near the main roadways have an increased incidence and severity of health problems that may be related with traffic emissions of air pollutants. The concentrations of near-road atmospheric pollutants vary depending on traffic patterns, environmental conditions, topography and the presence of roadside structures. In this study, the vertical and horizontal variation of nitrogen dioxide (NO2) and benzene (C6H6) concentration along a major city ring motorway were analysed. The main goal of this study is to try to establish a distance from this urban motorway considered “safe” concerning the air pollutants human heath limit values and to study the influence of the different forcing factors of the near road air pollutants transport and dispersion. Statistic significant differences (p=0.001, Kruskal–Wallis test) were observed between sub-domains for NO2 representing different conditions of traffic emission and pollutants dispersion, but not for C6H6 (p=0.335). Results also suggest significant lower concentrations recorded at 100m away from roadway than at the roadside for all campaigns (p<0.016 (NO2) and p<0.036 (C6H6), Mann–Whitney test). In order to have a “safe” life in homes located near motorways, the outdoor concentrations of NO2 must not exceed 44–60.0μgm−3 and C6H6 must not exceed 1.4–3.3μgm−3. However, at 100m away from roadway, 81.8% of NO2 receptors exceed the annual limit value of human health protection (40μgm−3) and at the roadside this value goes up to 95.5%. These findings suggest that the safe distance to an urban motorway roadside should be more at least 100m. This distance should be further studied before being used as a reference to develop articulated urban mobility and planning policies.