SWOV Senior Researcher Henk Stipdonk defended recently his PhD Thesis at Delft University of Technology, exploiting also findings from the EC co-funded research projects SafetyNet and Dacota. This Thesis, titled ‘Road safety bits and pieces: for a better understanding of the development of the number of road fatalities‘, focuses on the subdivision (stratification) of the crash data and the data of distance travelled. Different subgroups with different risks (like different travel modes, different age groups and combinations of both) are modelled separately. It is shown that these groups often have different risks and different trends in distance travelled. These different subgroups – the ‘bits’ and ‘pieces’ – and their different developments can give rise to a substantial change in the total risk – the ‘road safety’. It is concluded that the present manner of analyzing road safety developments – i.e. based on the total number of road fatalities and the total fatality rate – is insufficient to achieve a thorough understanding of these developments. It is better to divide the total number of road fatalities into subgroups and to investigate for each individual subgroup which factors influenced road safety.