Externalities from restrictions: Examining the short-run effects of urban core-focused driving restriction policies on air quality

To combat urban challenges such as air pollution stemming from excessive vehicle use, policy makers have adopted various driving restriction policies (DRPs) worldwide. Although previous studies have extensively justified the effects of citywide DRPs on air quality, little attention has been paid to urban core-focused license-plate-based DRPs (UCLDRPs), which have gained increasing popularity among major cities. To bridge this gap, we carried out an empirical evaluation of the short-run effectiveness of Shanghai's UCLDRPs in improving air quality using difference-in-differences (DID) modeling approaches on high-frequency air quality data. The results show that UCLDRPs did not lead to any reduction of air pollutants including NO2, PM2.5, and PM10 during peak hours (the restricted time window) in the inner ring area (the restricted area), while contributing to a 14% increase in the concentration of CO. Moreover, the air quality of surrounding zones (the 5 km buffer area) got worse as the concentration of CO and PM10 raised by 16% and 8% respectively. Results also justified the temporal-spatial spillover effects in the dynamics: the concentrations of CO and PM10 got increased by 10%-20% in the 5 km buffer area within time periods right before or after the restricted time windows.