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  1. Aug 2020
    1. In response to COVID-19, dramatic safer-​at-home policies were im­ple­mented. The un­der­stand­ing of their impacts on social dis­tanc­ing, travel and pollution is in its infancy. We pair a differences-​in-differences framework and synthetic control methods with rich cellular tracking and high frequency air pollution data. We find that state and U.S. county safer-​at-home policies are suc­cess­ful in en­cour­ag­ing social distance; beginning the day of the policy trips outside the home are sharply decreased while time in residence rises sharply. With less vehicle traffic, we find: a 50% reduction in vehicular col­li­sions; an ap­prox­i­mately 25% reduction in Par­tic­u­late Matter (PM2.5) con­cen­tra­tions; and a reduction of the incidence of county-​days with an air quality index of code yellow or above by two-​thirds. We calculate that the benefits from avoided car col­li­sions could range from $7 billion to $24 billion while the benefits from reduced pollution could range from $650 million to $13.8 billion.