Road accidents represent a huge social problem. Many of these accidents are preventable and by preventing them, society increases the supply of scarce resources that can be used to increase income and improve welfare. The study presented in this book is the first comprehensive study of the costs of road accidents in Portugal. The study is unique by presenting estimates of road accident costs for a period of fifteen years. During this period, road safety has been greatly improved in Portugal and the costs of road accidents have therefore been reduced. There are many ways of estimating road accident costs and no consensus exists regarding the best method. While the willingness-to-pay approach has many supporters, and from a theoretical point of view is the best approach, assessing willingness-to-pay empirically has turned out to be very difficult. Studies have been reported in many countries, but the results vary enormously. In view of this, there is a need for more research concerning how best to elicit willingness-to-pay for improved road safety. The root of the difficulties may, however, run deeper than many researchers are willing to admit. If people do not have clear preferences regarding the provision of road safety, and are easily influenced by the way valuation tasks have been framed, any estimate of the willingness-to- pay for less road accidents is bound to be very imprecise. This book has estimated the costs of road accidents by means of the human capital approach. The welfare effect, which many other studies try to estimate in terms of willingness-to-pay, is included by relying on court cases in which compensation has been paid for non-monetary damages. The costs presented in this book should be viewed as minimum estimates. The actual costs could be considerably higher, but are unlikely to be lower than estimated in this study. In addition to estimating the costs of accidents, the study includes an interesting analysis of factors that have influenced road safety in Portugal from 1988 to 2010. It is clear that some road safety initiatives taken in this period have been successful, others have not. It is important to systematically evaluate the effects of road safety measures in order to promote an optimal use of them. By studying historical experience both with respect to factors that have influenced road safety and changes in the cost of road accidents, an improved basis has been developed for amore effective road safety policy. It is to be hoped that policy makers will heed the lessons provided by this study. Rune Elvik Institute of Transport Economics, Oslo, Norway