SMU SOE Seminar (May 19, 2017): Subways and Urban Air Pollution

We investigate the relationship between the opening of a city’s subway network and its air quality. We find that particulate concentrations drop by about 5% in a 10km disk surrounding the city center during the year following a new subway system opening. The reduction in particulates is larger nearer the city center, but extends over the whole metropolitan area. The reduction persists over the longest time horizon that we can measure with our data, about eight years, although these estimates are less reliable further from the subway opening date. The 5% percent reduction is consistent with observed ridership in the subway system and induced reductions in automobile travel. Our results also point to decreasing returns to subway expansions, both in terms of particulate reduction and ridership. Using estimates from the literature on the relationship between particulates and infant mortality suggests that each subway rider provides and external health benefit of about 0.64 dollars per trip in the average city over at least the first 5-6 years after system opening. In the absence of pollution pricing, this provides a welfare basis for non-trivial public subsidies to subway ridership.

Keywords: Subways, Public transit, Air pollution, Aerosol optical depth

JEL Classification: L91, R4, R11, R14

Click here to view the paper.

Click here to view his CV.