Effect of Mandatory Bicycle Helmet Legislation on Helmet Use and Injury Outcomes: A Propensity Score-Matched Analysis...

Background: A non-penal bicycle helmet mandate was implemented in the Republic of Korea on 28 September 2018, yet post-implementation epidemiologic evidence remains limited. This study evaluated changes in helmet wearing and injury outcomes before and after the mandate and identified factors associated with helmet non-use. Methods: We conducted a retrospective observational study using Korea Trauma Data Bank records from January 2017 to December 2022. After exclusions, 7653 bicycle-injured patients were identified, and 1:1 optimal propensity score matching (caliper 0.10) produced 4798 patients (2399 pairs). Outcomes included helmet use, physiological status (AVPU scale and Revised Trauma Score), Injury Severity Score (ISS), Abbreviated Injury Scale by body region, and mortality. Monthly helmet use trends were analyzed using a regression tree to detect data-driven breakpoints and segmented logistic regression at the legal implementation point (22 months) and the regression-tree-identified split (19.5 months). Multivariable logistic regression identified factors independently associated with helmet non-use. Results: Helmet use increased modestly from 17.4% pre-mandate to 21.9% post-mandate (p < 0.001). Interrupted time-series analyses showed no immediate level or slope change at either breakpoint, suggesting gradual uptake. ISS values were higher post-mandate, with ISS > 15 increasing from 21.5% to 24.4% (p = 0.02). Total mortality rose from 3.9% to 5.3% (p = 0.02). Helmet non-use was independently associated with age 80-89 years, female sex, non-Korean nationality, and residence in Jeollabuk-do. Conclusions: The mandate was associated with a modest increase in helmet wearing without an abrupt behavioral shift. These findings suggest that legislation without enforcement may have limited impact as a stand-alone measure and should be complemented by targeted education, visitor-focused communication, and region-specific safety measures.