How a new metro line influences local traffic safety: A natural experiment in China

The introduction of a new rail transit system is expected to transform the travel behaviours of nearby residents and alleviate traffic congestion. However, the causal impacts of the rail transit system on traffic safety remain theoretically debatable, and the empirical evidence is limited. Leveraging the opening of a new metro line in a large Chinese city and longitudinal data on injurious traffic crashes covering both pre- and post-operation periods, this study provided causal evidence on how a new metro system affects traffic crashes in the vicinity of metro stations, including overall, pedestrian-involved, automobile-involved, and electric bicycle-involved injurious crashes. Treatment groups were defined as those experiencing a new metro service recently, while control groups were areas with a planned metro line and similar built environment attributes. Difference-in-differences (DID) models showed that the new metro line increases overall crash numbers by 14.0% and pedestrian-involved crash numbers by 13.8%, respectively, compared with the control groups after the metro operation. In addition, the treatment effects of the metro intervention on traffic crashes varied with the station location and the pre-intervention safety risk level. Our findings contribute causal evidence to ongoing debates regarding rail transit access and local traffic safety, and highlight the need for developing transport and planning integration for pedestrian safety in high-density cities.