A systematic review of quantitative assessments of traffic-focused urban air quality regulations

This systematic review follows PRISMA 2020 guidelines to identify whether measurable impacts have been observed following urban air quality interventions targeting private road users. A structured search was conducted on Scopus in February 2025, identifying 2088 studies. After applying strict inclusion criteria - requiring studies to examine urban-scale air quality interventions, target private road users, and apply quantitative ex post causal inference techniques - 59 studies were included for review. Our review examines publication trends, geographic focus, outlets, methods, key variables, and overall findings, classifying impacts on air quality, economic, behavioural, and health outcomes as positive, mixed, or negative. We identify three intervention types: (1) vehicle bans by type/time, (2) access charges for urban areas, and (3) fines for non-compliant vehicles. When splitting the papers by intervention type, outcome studied, and categorisation of impact, sample sizes become small. Only for intervention types (1) and (3), is there a sample of ≥ 10 studies examining the impacts on one outcome: air quality. Of these papers, a higher proportion examining fines for non-compliance found positive effects on air quality. While studies commonly report improvements in air quality and health, results are mixed for behavioural and economic variables. This review provides an up-to-date synthesis of policy effectiveness and highlights methodological and geographic gaps in the literature, supporting future evidence-based policy design.