Impact assessment of local traffic interventions on disease burden: A case study on paediatric asthma incidence in two European cities

Air pollution, particularly NO 2 , contributes to poor health, including paediatric asthma. This study estimated the reduction in NO 2 concentrations on annual car-free Sundays in two European cities, Brussels and Paris, which have extensive car-free zones (162 km 2 and 105 km 2 ). We then conducted health impact modelling of paediatric asthma incidence using a hypothesized expansion of annual car-free Sundays to car-free daily zones. Exposure to air pollution, particularly NO 2 exposure, contributes to negative health outcomes, including paediatric asthma. Local traffic interventions, such as car-free days, could offer a potential strategy to mitigate these effects. We assessed NO 2 concentration reductions using various methods, including (1) direct calculations, (2) direct calculations adjusted for meteorological conditions, (3) random forest modelling, and (4) boosted regression tree modelling. To estimate the reduction in paediatric asthma incidence, we applied existing Exposure Response Functions (ERFs) derived from epidemiological studies. These ERFs were used to quantify the relationship between NO 2 exposure and asthma incidence by linking the estimated reductions in NO 2 concentrations from our models to changes in health outcomes under exposure scenarios similar to the hypothetical case of permanent car-free days. NO 2 concentrations were significantly lower on car-free Sundays, with reductions ranging from 63 to 83% in selected areas of Brussels and 27–56% in selected areas of Paris. The health impact modelling indicated a reduction in paediatric asthma incidence ranging from 15% [95% CI: 11–19%] in residential areas of Brussels to 34% [95% CI: 25–41%] in heavily trafficked areas in Brussels, and from 15% [95% CI: 10–19%] to 19% [95% CI: 13–24%] in Paris for the hypothesized counterfactual scenario of daily car-free zones. Implementing car-free Sundays can strongly reduce NO 2 levels and result in lower paediatric asthma incidence if these local traffic intervention measures were to be expanded and implemented permanently. • Significant NO 2 reduction in Brussels and Paris with Local Traffic Interventions. • Consistent Results Across Multiple Assessment Methods. • Local Traffic interventions Could Reduce Asthma Incidence by 15–34% in European cities. • Methodology Applicable to Assess Other Pollutants and Diseases. • Need for further Interventional Studies with Accurate Monitoring.