Assessing the exposure to air pollution during transport in urban areas – Evidence review

Introduction: In recent years, questions have been asked about how people's exposure to air pollution varies across different transport modes, particularly in urban areas and how various factors, such as route choice and proximity to motorised transport for active travellers, characteristics of public transport vehicles, ventilation settings for cars and time of the day, may affect exposure. 

Methods: A comprehensive review was carried out to identify studies reporting measurements of pollutant concentrations in urban transport microenvironments published between January 2016 and July 2020 in Medline, Scopus and Embase databases. Average exposure values and ranges per transport mode were calculated, as well as the ratios of exposure between transport modes and factors within the same study. 

Results: Higher concentrations of air pollutants were often experienced in motorised transport compared to cycling and walking. However, closing car windows and operating ventilation in recirculation mode was found to lower particulate pollution concentrations inside cars. Pedestrians and cyclists were generally exposed to lower concentrations of air pollution when using routes separated from motorised traffic; the exposure of cyclists could be over three times higher when cycling on a high-traffic route compared to cycling on a traffic-free route and over four times higher when comparing cycling on-carriageway with cycling on a separated cycle lane. 

Conclusions: The consolidation of evidence from this review can inform consistent public health messaging as well as development of transport and planning policies in urban areas. Considering wider, long-term public health and environmental benefits, every effort should be made to prioritise active travel and public transport and enable more people to use these modes. Also, the COVID-19 pandemic has resulted in clear changes in travelling. Maintaining some of these changes, such as reductions in the numbers of unnecessary motorised trips could be beneficial through reductions in congestion and air pollution.