Helmet Laws, Helmet Use, and Bicycle Ridership

To assess bicycle helmet laws' effect on helmet and bicycle use among U.S. high school students in urban jurisdictions.

Log-binomial models were fit to Youth Risk Behavior Survey data from five jurisdictions. Adjusted helmet and bicycle use proportions were calculated with post-regression marginal effects. Difference-in-differences were estimated, comparing intervention to concurrent controls. A placebo outcome was used to falsify possible confounding or selection effects.

In San Diego and Dallas, helmet use increase increased 10.6 (95% confidence interval [CI] 6.5 to 14.7, p < .001) and 8.1 (95% CI 4.3 to 12.0, p < .001) percentage points more than out-of-jurisdiction controls. Increases in Florida counties were 5.0 (95% CI 1.8 to 8.2, p = .003) and 4.0 (95% CI -.7 to 8.8, p = .098) points against age-based and out-of-jurisdiction controls, respectively. Bicycle use fell 5.5 points in both San Diego (95% CI -9.8 to -1.1, p = .015) and the Florida counties (95% CI -11.5 to .5, p = .075) against out-of-jurisdiction controls, but other comparisons had no significant changes. The placebo outcome never changed significantly.

Laws increased helmet use in all jurisdictions, with limited evidence of reduced cycling. Although sound health policy, laws should be coupled with physical activity promotion.