Topic: “Restricting Driving for Better Traffic and Cleaner Sky: Did It Work in Beijing?”Abstract: Driving restrictions have been implemented in a number of cities across the world. However, limited by data gaps and the potential problems in the prevailing research methodology of regression discontinuity, few studies have quantitatively proven driving restrictions’ effects on traffic and researchers disagree on the air quality consequences of driving restrictions. For the first time in similar studies, we introduce data measuring traffic conditions, which provide insights on the complicated policy process from driving restrictions to changes in traffic, emissions, and air quality. To more reliably identify driving restriction’s marginal effects than the existing studies, we take advantage of the Chinese cultural resentment toward the number “four” and use the unequal stringency of alternative restriction numbers as repeated exogenous treatments. We find that Beijing’s “one-day-per-week” driving restrictions reduced city-wide traffic delays but showed little effect on the concentration of inhalable particulates. We proposed and examined four possible explanations. We find that likely due to the nonmonotonic relationship between network-level traffic speed and total traffic volume, marginal improvements in traffic conditions may have little or even negative effects on air quality, given Beijing’s extremely congested roads. This implies that positive traffic and environmental effects of a policy may not always go hand in hand. To significantly reduce automobile emissions and improve air quality in a heavily congested city like Beijing, measures other than the one-day-per-week driving restriction are necessary.Professor Rui Wang’s research focuses on the policy analysis of sustainable urban development, particularly green transportation, climate change, air quality, public health, and environmental economic geography in the U.S. and/or China. His work appears in academic outlets such asAtmospheric Environment, Environment and Planning C: Government and Policy, Journal of Economic Geography, Journal of Real Estate Finance and Economics, Transport Policy, and Urban Affairs Review. Professor Wang teaches “Introduction to Environmental Policy” and “Transportation and the Environment” in the Departments of Public Policy and Urban Planning, directs the UCLA Chinese Planning Professional Training Program, and serves on the Editorial Board of U.S. DOT’sJournal of Transportation and Statistics.