Background <p>With the global rise in the aging population, ensuring safe mobility for older adults is an urgent public health concern. In Taiwan, scooters are widely used by older individuals, yet the impact of air pollution, particularly fine particulate matter (PM_2.5), on their traffic safety remains poorly understood. This study investigated the short-term association between PM_2.5 exposure and the risk of scooter collisions among older adults.</p> Methods <p>We conducted a nationwide time-series analysis using Taiwan’s Police-Reported Traffic Accident Registry and air quality monitoring data from 2023. The study included 58,181 scooter riders aged ≥ 65 years involved in collisions. Daily PM_2.5 concentrations were derived from over 70 monitoring stations. We applied distributed lag non-linear models (DLNM) with a negative binomial distribution to estimate the association between PM_2.5 exposure and daily scooter collision counts, adjusting for meteorological variables, co-pollutants (NO₂ and SO₂), and temporal variables. The models accounted for both same-day exposure and cumulative effect of exposure across lag periods of up to 14 days.</p> Results <p>We found that 159 older adults were involved in scooter collisions per day on average, with a mean PM_2.5 level of 13.4&#xa0;µg/m³. A non-linear exposure-response relationship was observed, with rate ratios increased at PM_2.5 levels ≥ 20&#xa0;µg/m³, particularly over longer lag periods. The highest risk estimate was observed for 15-day cumulative exposure at 31&#xa0;µg/m³ (rate ratio = 2.357; 95% CI: 1.419–3.914). In contrast, same-day exposure showed a limited association with collision risk.</p> Conclusions <p>These findings suggest that prolonged exposure to elevated PM_2.5 may increase the risk of scooter collisions among older adults, highlighting the need to integrate air quality considerations into traffic safety strategies for aging populations.</p>