Identifying peer states for transportation policy analysis with an application to New York's handheld cell phone ban

There has been a significant amount of research in the transportation area on the development of strategies that allow good comparisons between states, such that policy analysis are allowed to be carried out and informative policy-oriented questions are allowed to be answered. In this article, the use of Synthetic Control Methods (SCM) is proposed to overcome several identification problems present in previous studies when constructing comparison groups/counterfactuals. The SCM is used to analyse the effect of New York state's law prohibiting handheld cell phone use while driving on fatality rates. Results show that (i) a synthetic peer state' for NY when evaluating this specific policy is composed of a convex combination of the states of IL, MA and TX and (ii) that imposing the ban led to a decrease of about 9% in fatality rates.