Road safety policies should undergo performance and efficiency evaluations. Such evaluations cannot be undertaken without Crash Modification Functions (CMFs). Evaluation processes should be documented to ensure they are transparent.

The decision making process for safety interventions is complex, involving a number of actors (experts, public, politicians, etc.) and issues (environment, economy, congestion) competing for the scarce resources available. The risk of making poor decisions and the cost of making better decisions can be reduced by the use of reliable studies on how effective different safety measures are (i.e. Crash Modification Functions – CMFs).

The decision making process for safety interventions is complex, involving a number of actors (experts, public, politicians etc) and issues (environment, economy, congestion) competing for the scarce resources available. The risk of making poor decisions and the cost of making better decisions can be reduced by the use of reliable studies on how effective different safety measures are (ie. Crash Modification Functions – CMFs).

Each year about 1.3 million people are killed and another 50 million people are injured on roads worldwide. These road crashes cost countries between 1 and 3 percent of their Gross Domestic Product (WHO, 2010). In addition, they cause great emotional and financial stress to the millions of families that are affected by these crashes. A lot of these crashes can be prevented by implementing effective road safety measures. To be able to select the best measure, a decision maker needs information about the effectiveness of different measures. Moreover, information about the effectiveness of measures is needed in case one (a politician) has to make a choice between expenses on road safety measures and other expenses, like measures to limit environmental effects of traffic or measures to improve traffic throughput.

This chapter reviews some of the technical challenges for international collaboration on crash modification functions. The chapter identifies opportunities to overcome obstacles for the transferability of road safety knowledge and encourage positive action to support transferability. It discusses the importance of the proper planning and documentation of research in improving international transferability of CMFs.

This chapter introduces a statistical technique for assessing the transferability (external validity) of road safety evaluation studies from one country to another. The technique can be used to calculate statistics showing the consistency in time and space of studies that have evaluated the effects of road safety measures. The method is illustrated through a number of examples.

This chapter provides a quantitative framework for assessing and enhancing the international transferability of crash modification functions. Variability in CMF research results is identified as a major deterrent to international transferability. The chapter provides detailed guidance on how to assess variance. It further describes how researchers can build studies to reduce variance from this perspective and how practitioners can better understand CMFs that they would like to apply.

This chapter discusses some of the challenges of safety decision making and provides an illustration on how Crash Modification Functions can support decision making to overcome some of these barriers. One of the hindrances to the widespread use and transfer of CMS is the lack of supporting documentation related to the countermeasure, the development process, and conditions under which the countermeasure was tested. The chapter provides a list of essential reporting elements for inclusion in any study presenting safety evaluation results. Finally, this chapter also discusses the underlying conditions required for sharing knowledge of effective safety policies with developing countries.

This report has highlighted the complex nature of decision making for sound investments in road safety. Among other items, crash modification factors or functions (CMFs) that relate safety effectiveness to interventions and are transferable from one situation to another are a valuable tool in spreading effective safety policies. CMFs are fundamental to identifying the most effective road safety countermeasures and for conducting economic analysis of safety policies. Demand for CMFs is growing in many jurisdictions as policy makers increase their requirements to demonstrate results and undertake cost-benefit and efficiency assessments and as managers seek to ensure they are making the best possible decisions for safety in their projects.

This appendix provides a review of national and international approaches for the efficiency assessment of road safety measures. In particular, the most important international initiatives for providing standardized and accurate methods or tools for the estimation of safety effects of road safety measures are presented. Furthermore, examples from the use and application of these (or other) methods and tools at national level are analyzed.