The objective of this project is to develop a synthesis on best practices on cost-effective road safety investments, based on the information/data collected and analysed within the CEDR O7 Group. Initially in this project, a review of the current methodologies and practices dealing with cost-effectiveness studies of road safety investments both in EU and worldwide will take place in order to get a good knowledge of the current state-of-the-art of road related safety measures. Based on the results of the review and the analysis of the relevant information, selected road related safety investments will be further assessed, and more specifically, the key elements determining the level of the various interventions’ efficiency will be identified and further examined. Appropriate cost-effectiveness ratios will be calculated, taking into account the safety effect and the implementation costs of the investments, but also the conditions under which these are implemented. The selected road related safety investments will be ranked and the most cost – effective of them will be further analysed in order to identify their strengths, weaknesses, as well as the barriers to their application and the results of their implementation on the road safety level and on the road user’s behaviour. The final output of the project could be used as a reference by any road authority wishing to justify the selection of the most appropriate road related intervention.