Urban Rail Transit Can Improve Air Quality: New Evidence from Chinese Cities

In this research, we investigate whether urban rail transit expansion improves air quality. We also compare the magnitudes of the effects across cities and explain the variation. The results suggest that opening subways alleviated air pollution, especially during non-rush hours in the daytime. We find that the effects are smaller in the cities with higher income and more subway lines, while the effects are larger in the cities with higher population density. Furthermore, the effect of the first subway line opening is stronger, compared to expansion of an existing subway system.