Background The Centres for Disease Control and Prevention have recognised the United States’ reduction in motor vehicle fatalities as one of the 20^th century’s greatest public health achievements. Public policy played a critical role in this progress. Regulatory oversight and public investment yielded safer vehicles and modern highways. State legislation was passed to encourage members of the public to drive safely and use protective equipment. Many jurisdictions however, both within the United States and internationally, are not benefitting from policies that have been shown to save lives. The purpose of this study was to increase our understanding of the barriers that prevent legislators from adopting evidence-based traffic safety policies.

Methods A review of legislative activity was carried in the 2013 and 2014 to identify traffic safety bills under consideration at state legislatures within the United States. Four bills were selected for study inclusion because there was scientific evidence that suggests they would likely have influenced injury outcomes, and they had received mixed votes within the state’s legislative body. Legislators who had voted for and against the bills were invited to participate in semi-structured interviews. Discussions were audiotaped, and subsequently transcribed. They were then coded for themes. A sample of the data was also coded by a second reviewer, to ensure that a reliable coding scheme had been developed.

Results The characteristics of legislators who agreed and declined to participate in the study will be reported. The perspectives of policymakers who voted for and against the proposed safety laws will be contrasted, with regard to issue salience, factors influencing their vote, whether interest groups or constituents contacted them and what they believed that the consequences of the bill’s passage would have been. General legislative insights into what safety advocates need to understand about a policymaker’s perspective will also be presented.

Conclusions Many factors other than scientific evidence influence whether legislators support important safety legislation. More research is needed into how to overcome value-driven objections. Safety advocates would benefit from a more sophisticated understanding of the legislative process, and/or partnering with professionals who are more familiar with the policymaking environment.