The Effect of Smog – Ozone Warnings and a Vanpool Program on Traffic Volume in York County of South Carolina

Ground-level ozone is a critical criteria pollutant that is significantly generated by transportation patterns. We study the effect of smog-ozone warnings, triggered by the Environmental Protection Agency, on traffic volume in York County, South Carolina during the period 2006-10. In addition, the subperiods 2006-07 and 2008-10, where the ozone smog-alert thresholds 0.080 parts per million (ppm) and 0.075 ppm, respectively, are examined. The approach followed in this paper is a differences-in-differences (DID) regression. Additionally, a regression discontinuity design in the DID framework is applied. We find a negative and significant decrease in weekday peak-hour traffic volume in the treatment group during 2008-2010