I am trained as an environmental economist, and I have a particular interest in urban transportation applications. The broad theme of my research is the interaction between regulation and provision of infrastructure and how existing regulatory policies influence public transit investment decisions. I am currently beginning to study land use regulation and zoning policies, and the interaction with the transportation sector.
The Effects of Public Transit Supply on the Demand for Automobile Travel (working paper: pdf), (Journal of Environmental Economics and Management, 88 (2018): 447-467), with C.-Y. Cynthia Lin Lawell.
Public transit is often advocated as a means to address traffic congestion within urban transportation networks. We estimate the effect of past public transit investment on the demand for automobile transportation 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. The results show that, after controlling for the underlying factors that generate auto traffic growth, increases in public transit supply lead to a small overall reduction in auto travel volumes. In the short run, when accounting for the substitution effect only, we find that on average a 10% increase in transit capacity leads to a 0.8% reduction in auto travel in the short run. However, in the longer run, when accounting for both the substitution effect and the induced demand effect, we find that on average a 10% increase in transit capacity is expected to lead to a 0.3% reduction in auto travel. We also find that traffic congestion needs to exceed a threshold level before public transit supply begins to potentially reduce auto travel. Additionally, we find that there is substantial heterogeneity across urban areas, with public transit having significantly different effects on auto travel demand for smaller, less densely populated regions with less-developed public transit networks than for larger, more densely populated regions with extensive public transit networks.
Is Public Transit's `Green' Reputation Deserved? Evaluating the Effects of Transit Supply on Air Quality (working paper: pdf), with C.-Y. Cynthia Lin Lawell.
In recent decades, air quality in the U.S. has improved substantially. Over this time, there has been also been a steady increase in the volume of transit capacity supplied. 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. In this paper, we ask 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. To answer this question, we develop 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 for 96 urban areas across the U.S. In particular, we analyze the effects of the level of transit supply on the following criteria pollutants: carbon monoxide (CO), lead (Pb), nitrogen dioxide (NO2), ozone (O3), particulate matter (PM), and sulfur dioxide (SO2). 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 Investment and Traffic Congestion Policy (working paper: pdf), with Y. Hossein Farzin and C.-Y. Cynthia Lin Lawell.
This paper develops a theoretical model to analyze what role, if any, public transit investment should play in traffic congestion policy. In particular, we evaluate the extent to which traffic congestion should be accounted for when evaluating investment in public transit infrastructure when a Pigouvian congestion tax cannot be levied on auto travel. Our second-best model of public transit investment contributes to the literature by allowing for both demand and cost interdependencies across the auto and transit modes. The results indicate that the level of transit investment should be higher relative to that chosen when the congestion-reduction effects of transit are not accounted for, but the importance of this consideration is dependent upon the interaction of demand and cost interdependencies across the auto and transit modes, which may vary across regions.
Public transit investment and sustainable transportation: A review of studies of transit's impact on traffic congestion and air quality (Research in Transportation Economics, 52 (2015): 15-22, pdf), with Y. Hossein Farzin and C.-Y. Cynthia Lin Lawell.
In this paper we provide a framework for evaluating public transit investment, taking account of the effects of transit investment on traffic congestion and air quality. We discuss how to assess the sustainability of transit investment and the mechanisms through which public transit investment can affect equilibrium auto travel volumes and the associated congestion and air quality outcomes. Several related issues are addressed: the differences between short-run and long-run equilibria; the role of regional heterogeneity; regulatory and policy considerations; and the potential endogeneity of transit investment when conducting empirical analyses. As the transportation policy landscape evolves and technological advancements continue, a complete evaluation of the social benefits of transit investment is essential both for allocating investment funds and for designing policies that result in an efficient level of investment and travel in the long run. Does the existing evidence bolster public transit's 'green' reputation? Reviewing the recent empirical literature, it appears that transit can both reduce congestion and improve air quality, but the magnitudes of these benefits are uncertain and may be specific to each location.