Regional trains and air pollution: estimating avoided NO ₂ concentrations through a natural experiment

Abstract Regional rail services offer a cleaner alternative to private road vehicles, contributing to environmental quality in terms of reduced pollution. However, air pollutant concentrations reductions are not observable, and the related environmental benefits provided by the train service might be underestimated. Our research quantifies the emission reductions attributable to regional rail services by exploiting a natural experiment. We leverage an unexpected accident in Florence that temporarily disrupted part of the Tuscan railway network. We find that affected areas experienced, on average, a 25% increase in NO₂ pollution compared to counterfactual areas where train services remained operational. This increase was most pronounced during peak commuting hours. These findings are consistent with the assumption of substitutability between public and private transport: when regional trains were unavailable, more people had to switch to private vehicles to commute, causing a rise in local pollution. Our study provides an indirect measure of the positive environmental impact of public transport.