Urban bike and pedestrian activity impacts from wildfire smoke events in Seattle, WA

Introduction: Climate change is leading to increasingly severe wildfires across the United States. Over the past several years, these events have led to extreme, persistent smoke events in several urban areas across the western U.S. However, the health impacts of smoke events on urban communities are not well understood. Impacts to physical activity, including active transportation, may be a useful proxy to understand physical and mental health effects of these events. We aimed to examine the impact of wildfire smoke events, determined by fine particulate matter concentrations and administrative reporting, on physical activity, measured by pedestrian and bicycle counts at eight city counters in Seattle, WA, USA. Methods: We assessed for differences in daily average bicycle and pedestrian counts between pre-, during- and post-wildfire smoke periods for two wildfire smoke events in Seattle in the summers of 2017 and 2018. Results: The 2018 wildfire smoke event significantly decreased daily average bicycle counts by 14.6-36.0% across the 8 counters, and 31.7%-45.2% across the two pedestrian counters. There were no significant changes in use during the 2017 event, with the exception of a significant decrease in counts at one pedestrian counter. Conclusions: Urban physical activity and active transportation may be significantly impacted by future wildfire smoke events, with cascading public health consequences. Differences in impacts across the 2017 and 2018 events may be related to increased intensity of smoke, and/or to enhanced public health messaging by state and local agencies. Additional research is needed to better understand the impact of wildfire smoke on physical activity in urban communities, and to assess and inform public health risk communication campaigns to change behavior during these events.