Impact of helmet laws on motorcycle crash mortality rates

BACKGROUND: Helmets are effective in reducing traumatic brain injury. However, population effects of helmet laws have not been well described. This study assesses the impact of helmet laws on the motorcycle (MC) fatality rate in the United States from 1999 to 2015. METHODS: Fatality Analysis Reporting System MC fatalities (aged ≥16 years), crash characteristics, and MC-related laws were collected by year for all 50 states from 1999 to 2015 to create a pooled time series. Generalized linear autoregressive modeling was applied to assess the relative contribution of helmet laws to the MC fatality rate while controlling for other major driver laws and crash characteristics. RESULTS: Universal helmet laws were associated with a 36% to 45% decline in the motorcycle crash mortality rate during the study period across all age cohorts (unstandardized regression coefficients are reported): 16 to 20 years, B = -0.45 (p < 0.05); 21 to 55 years, B = -0.42 (p < 0.001); 56 to 65 years, B = -0.38 (p < 0.04); and older than 65 years, B = -0.36 (p < 0.02). Partial helmet laws were associated with a 1% to 81% increase in the fatality rate compared with states with no helmet laws and a 22% to 45% increase compared with universal laws. Helmet usage did not attenuate the countervailing effect of weaker partial laws for 16 to 20 years (B = 0.01 p < 0.001). Other laws associated with a declining motorcycle crash mortality rate included the following: social host/overservice laws, 21 to 55 years (B = -0.38 p < 0.001); 56 to 65 years (B = -0.16 p < 0.002), and older than 65 years (B = -0.12 p < 0.003); laws reducing allowable blood alcohol content, 21 to 55 years (B = -4.9 p < 0.02); and laws limiting passengers for new drivers 16 to 20 years (B = -0.06 p < 0.01). CONCLUSION: During the period of the study, universal helmet laws were associated with a declining mortality rate, while partial helmet laws were associated with an increasing mortality rate. Other state driver laws were also associated with a declining rate. In addition to universal helmet laws, advocating for strict alcohol control legislation and reevaluation of licenses in older riders could also result in significant reduction in MC-related mortality. LEVEL OF EVIDENCE: Prognostic and epidemiological, level III.