Air quality alert and traffic reduction: Potential alteration by travel option

Citizen behavior change can serve as an important contributor to improving air quality, when the change is related to traffic emission considered as a major source of air pollution. This study aimed to examine the shift of traffic counts attributed by the Emergency Fine Dust Reduction Measures (EFDRM) in Seoul, South Korea, where one of the major components is text alert service to promote public engagement. Specifically, we investigated the changes in traffic counts before and during EFDRM as well as between different hours and days of the week which could affect people's travel mode choices. We obtained hourly traffic counts, fine particle concentrations, and meteorological conditions in Seoul for 2016-2019. Using the difference-in-difference design and generalized additive model, we estimated the differences in traffic counts between the days with and without the EFDRM and between pre- and post-implementation periods after adjusting for fine particle air pollution, meteorology, and temporal trends. In addition, we compared these differences by rush and non-rush hours and by weekdays and weekends/holidays in order to examine the changes in travel behavior. The traffic counts on EFDRM days were significantly lower than on non-EFDRM days after the implementation, whereas no systematic reduction was observed before the implementation. This decrease was found on weekends/holidays and during weekday non-rush hours, but not during weekday rush hours, indicating the impact of the feasibility on behavioral changes in addition to perception. Our findings suggest that short-term air quality interventions can achieve the goal when accompanied with public communication targeting the alternative travel option.Implications: This study provides new evidence that short-term emergency actions can effectively reduce traffic counts through citizen behavioral changes. The findings highlight that the involvement of public communication and feasible alternative travel options to short-term actions can play an important role in the success of interventions. The reduction in traffic counts, particularly during non-rush hours and weekends, suggests that voluntary behavioral responses can contribute to improving air quality without imposing large regulatory costs. These results offer practical guidance for policymakers to design public engagement - based air quality measures and indicate that similar alert systems could be applied to other pollutants or urban contexts worldwide.