Air Quality Evidence in Road and Rail Transport Corridors: A Comparative Systematic Mapping Review

Aerosol emission and dispersion in transport corridors are central to urban air quality, human exposure assessment and transport planning. Although near-road air pollution has been widely studied, much less is known about analogous processes in rail-related environments, especially in at-grade and semi-open rail corridors. This study presents a comparative systematic mapping review of evidence on air quality, with a focus on aerosol emission, dispersion and exposure in road and rail transport corridors. The literature search was conducted in Scopus, Web of Science Core Collection and PubMed for publications published between 2000 and 28 June 2026, using a PRISMA-based screening procedure. A total of 2958 records were identified. After deduplication, 1693 records were screened, and 1431 records were retained for thematic analysis. Retained set consisted of 885 road/near-road only records, 337 rail/near-rail only records, 193 shared/comparative records and 16 records assigned to other transport microenvironments. The road literature was well developed in relation to concentration gradients, dispersion, monitoring, modelling and exposure assessment. In contrast, the rail literature was dominated by metro systems, underground railways, tunnels and underground stations, which accounted for 435 records, or 82.1% of rail-related records. Only 95 rail records addressed at-grade, open, semi-open or general rail environments. The main research gap concerns aerosol emission, dispersion and human exposure in at-grade railway, tram and light rail corridors.