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Abstract

We study an air quality alert program that informs the public of high ambient air pollution levels and broadcasts a Don't Drive Appeal (DDA) to encourage motorists not to drive on poor air quality days. We use fixed effects panel models and a rigorous sub-sampling method to analyze 28 months of traffic data from Stuttgart, Germany and evaluate whether DDAs reduce driving. We find DDAs inadvertently increase driving by up to 2% in Greater Stuttgart. This overall effect is driven by heightened weekend and periphery traffic during DDAs. Notably, DDAs successfully reduce city center traffic on some weekdays and for the first five days of DDA events. However, estimated traffic reductions never exceed 5% of daily traffic flows, suggesting that high switching costs and dynamic norm factors may deter most motorists from choosing the DDA's desired response. These results provide cautionary evidence about implementing DDAs to reduce driving.