<p>With changing trends in drug misuse in the United States, including the increased prominence of fentanyl misuse, transit operators have indicated concern that people who use drugs (PWUD) seek transit vehicles as shelter to escape from inclement weather. Research has yet to investigate the relationship between drug misuse on transit vehicles and weather conditions. We hypothesized that there would be a higher frequency of drug use incidents on transit vehicles during periods of reduced daylight hours, low temperatures, high precipitation, or high wind speeds. Using a dataset of drug use incidents reported by transit operators in King County, Washington, in 2022 (<i>n</i> = 1518), we descriptively characterized the frequency of daily drug use incidents. We used a Poisson regression model to further understand the association between daily incident count and daily weather patterns. Reported drug use incidents showed clear temporal trends, with a higher frequency of incidents in winter and spring than in summer; April had the highest mean daily incident count of 7.3 incidents/day. Higher temperature was significantly associated with lower incident count (IRR, 0.96; 95% CI, 0.95, 0.97). Daylight hours were also significantly positively associated with higher incident counts (IRR, 1.14; 95% CI, 1.11, 1.17). The findings of this study support the hypothesis that drug use incidents are more common on days with lower temperatures. These results can help guide the timely deployment of interventions, informed by drug use patterns, to reduce drug use incidents on transit and reduce operator and passenger exposure to secondhand drug use.</p>