The Unintended Consequences of Regulation in the Presence of Multiple Unpriced Externalities: Evidence from the Transportation Sector
研究加州允许单人低排放车辆使用拼车道的政策，发现其因加剧拥堵导致福利净损失，环境效益远低于拥堵成本，每吨温室气体减排成本高达124美元。
In transportation systems with unpriced congestion, allowing single-occupant low-emission vehicles in high occupancy vehicle (HOV) lanes to encourage their adoption exacerbates congestion costs for carpoolers. The resulting welfare effects of the policy are negative, with environmental benefits overwhelmingly dominated by the increased congestion costs. Exploiting the introduction of the Clean Air Vehicle Stickers policy in California with a regression discontinuity design, our results imply a best-case cost of $124 per ton of reductions in greenhouse gases, $606,000 dollars per ton of nitrogen oxides reduction, and $505,000 dollars per ton of hydrocarbon reduction, exceeding those of other options readily available to policymakers. For reasons discussed in Harberger (1974), the estimation of the overall welfare effects of government interventions to correct externalities is more challenging * Bento: Cornell University, Charles H Dyson School of Applied Economics and Management. 424 Warren Hall, Ithaca, NY 14853 (e-mail: amb396@cornell.edu); Kaffine: University of Colorado Boulder Department of Economics, Econ 11, Boulder, CO 80309 (email: daniel.kaffine@colorado.edu); Roth: University of California, Irvine, Department of Economics, 3151 Social Science Plaza, Irvine, CA 92697 (email: kroth1@uci.edu); Zaragoza-Watkins: University of California at Berkeley, Agricultural and Resource Economics, 207 Giannini Hall, Berkeley, CA 94720 (email: mdzwatkins@berkeley.edu). The authors thank Richard Arnott, Lucas Davis, Mary Evans, Matthew Freedman, Kenneth Gillingham, Sumeet Gulati, Ryan Kellogg, Shanjun Li, Jordan Matsudaria, Justin McCrary, Erich Muehlegger, James Sallee, and Hendrik Wolff for helpful comments as well as seminar participants at AERE-Seattle 2011, Colorado School of Mines, Columbia, EAERE 2011, Inter-American Development Bank, Oregon State University, Stanford, TREE Seminar Series, UC-Berkeley, University of Connecticut, UEA-Miami 2011, WCERE-Montreal 2010, and Yale. Finally we thank Arthur T Degaetano for weather data.