Air quality alerts and don’t drive appeals: Evidence on voluntary pollution mitigation dynamics from Germany

This paper studies temporal factors influencing the effectiveness of prosocial appeals used by policy-makers to encourage motorists to voluntarily reduce driving during temporary high pollution episodes. We derive and empirically validate a theoretical framework for repeated multi-day appeals where the desired behavioral response is sensitive to the number of consecutive appeal days and time intervals between appeal events. Our difference-in-differences event study analysis of traffic flows in Stuttgart, Germany shows appeals reduce traffic by about 3 % on the first three appeal days, but effectiveness tapers off during prolonged activation. Moreover, appeals reduce traffic by about 5 % following a lengthy time interval between appeals and are effective once authorities announce when they will be lifted. Our findings confirm prior North American evidence of limited appeal effectiveness in a novel European setting and highlight the relevance of dynamic temporal factors for voluntary short-term pollution mitigation programs.