Friday Transportation Seminar: Is Public Transit's 'Green' Reputation Deserved?
Friday, November 2, 2018 - 12:00pm

Friday Transportation Seminars at Portland State University have been a tradition since 2000, hosted by the Transportation Research and Education Center in partnership with the College of Urban & Public Affairs and the Maseeh College of Engineering and Computer Science. See all Friday Transportation Seminars


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.



  • 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, University of Washington Tacoma

    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.

    Transportation Research & Education Center

    The Transportation Research and Education Center (TREC) at Portland State University is home to the National Institute for Transportation and Communities (NITC), the Initiative for Bicycle and Pedestrian Innovation (IBPI), and other transportation programs. TREC produces research and tools for transportation decision makers, develops K-12 curriculum to expand the diversity and capacity of the workforce, and engages students and young professionals through education.

    Friday Transportation Seminars are recorded and archived on the TREC website. Click here to acccess the archive of past seminars.

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