While public transit has a reputation as a potential means to ameliorate the adverse environmental effects of automobile travel, there have been very few empirical studies of the marginal effect of transit supply on air quality. We explore whether any of the substantial improvement in air quality observed in the U.S. from 1991 to 2011 can be attributed to increased public transit supply by developing an equilibrium model of transit and automobile travel volumes as a function of the level of transit supplied. We then empirically analyze the effects of the level of transit supply on observed ambient pollution levels by applying an instrumental variables approach that accounts for the potential endogeneity of public transit investment to a panel dataset of 96 urban areas across the U.S. over the years 1991-2011. We analyze the effects of the level of transit supply on the following criteria pollutants: carbon monoxide, nitrogen dioxide, ozone, particulate matter, and sulfur dioxide. We find that - at the margin, and given existing urban travel regulations in place - there is no evidence that increased transit supply improves air quality; in fact, transit appears to lead to a small deterioration in overall air quality.
KEY LEARNING OUTCOMES
- Public transit appears to be less "environmentally friendly" than typically thought.
- The effect of transit supply on air quality varies by region and pollutant.
- Environmental impacts should be a relatively minor consideration when evaluating potential transit investments.
Justin Beaudoin is an Assistant Professor of economics in the School of Interdisciplinary Arts & Sciences at the University of Washington Tacoma. He earned his PhD in Agricultural and Resource Economics from the University of California, Davis in 2015. His research focuses on the intersection of urban and environmental economics, with a particular interest in the evaluation of public transit investments.
This 60-minute seminar is eligible for 1 hour of professional development credit for AICP (see our provider summary). We provide an electronic attendance certificate for other types of certification maintenance.
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