Weathering the ride: Associations of heat, smoke, precipitation, and ozone with bus ridership in Coloradoof temperature in Denver, Colorado

Key Words: Heat • Precipitation • Wildfire smoke • Bus ridership • Free fare policies • Front range

The study, published in Environmental Research and co-authored by faculty member Elizabeth Dzwonczyk, analyzes system-wide hourly bus ridership in the Denver metropolitan area from June 2022 through September 2023 to evaluate how short-term weather variability and air quality events shape public transit behavior. Utilizing fixed-effects negative binomial distributed lag nonlinear models, researchers modeled the immediate and delayed impacts of temperature stress, precipitation, ozone exceedances, and wildfire smoke while accounting for contextual modifiers like fare policy and shelter availability. The findings revealed that cold thermal stress caused the largest and most persistent cumulative drops in ridership, whereas precipitation prompted sharp but short-lived reductions concentrated within a few hours. While ambient air quality events like wildfire smoke showed limited impact overall, zero-fare policies and stop-level shelter infrastructure significantly modified weather-related ridership declines. Ultimately, this research provides transit agencies with actionable strategies to enhance public transportation resilience and maintain reliable service under increasing climate variability.

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