The objective of this paper is to develop a comprehensive synthesis on current challenges and opportunities for the assessment of the effectiveness of road safety measures worldwide, with focus on the potential for transferability.  This synthesis comprises the preliminary results of the work carried out in the framework of the on-going Working Group on the assessment of the effectiveness of road safety measures, of the Joint Transport Research Centre (JTRC) of the Organisation for Economic Cooperation and Development (OECD) and the International Transport Forum (ITF). Appropriate data and statistical evaluation methodologies together with systematic procedures and exchange of assessment results are considered as the prerequisites for acquiring the necessary knowledge, on which decision makers could rely for their decisions.  An opportunity for producing more reliable efficiency assessment results is the intensification of international cooperation both at the methodology and at the results level allowing to maximize research investments among countries and more rapid global dissemination and use of life saving countermeasures. Governments are therefore challenged to set policies or establish guidelines that will help improve the overall quality of effectiveness assessment research and results.