In order to improve road safety, availability of accident data and an understanding of the circumstances that lead to crashes are of vital importance.

The purpose of Road Accident Investigation (RAI) is to help road engineers detect road infrastructure deficiencies that influence an accident, in order to guide them in drafting a preference list of improvement interventions or of black spot treatments, and in designing appropriate improvement measures.

The report describes the accident data needed how the location of crashes should be reported and how accident data should be assessed. Focus is placed on collision diagram and on their analysis. A number of examples are presented in the appendices to illustrate the different situations.