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

Introduction

Air pollution, particularly NO₂, contributes to poor health, including paediatric asthma. This study estimated the reduction in NO₂ concentrations on annual car-free Sundays in two European cities, Brussels and Paris, which have extensive car-free zones (162 km² and 105 km²). We then conducted health impact modelling of paediatric asthma incidence using a hypothesized expansion of annual car-free Sundays to car-free daily zones.

Problem statement

Exposure to air pollution, particularly NO₂ 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.

Methods

We assessed NO₂ 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 NO₂ exposure and asthma incidence by linking the estimated reductions in NO₂ concentrations from our models to changes in health outcomes under exposure scenarios similar to the hypothetical case of permanent car-free days.

Results

NO₂ 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.

Conclusion

Implementing car-free Sundays can strongly reduce NO₂ levels and result in lower paediatric asthma incidence if these local traffic intervention measures were to be expanded and implemented permanently.