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This study describes the state of knowledge in terms of speed distribution and traffic safety. Real changes in speed-distribution and estimated accident risk for three different traffic safety measures are studied. The aim is to gain a better understanding of the relation between speed distribution and traffic safety. The study consists of: a literature review on models for the relationship between speed and accident risk, a study on the relation between measures from the speed distribution of different traffic safety measures and a study comparing different models that estimate accident risk. The literature review shows that several studies during the 1960s and 1970s that analysed individual risks in relation to the choice of speed showed a U-shaped relationship between speed and accident risk. More recent studies suggest that the relationship is rather monotonically increasing where the slope becomes steeper for higher speeds. This means that there is an increased risk of being involved in an accident for higher speeds. However, there is no overall increased risk if you drive slower than the average speed on the road. In the second study it is shown that measures like new speed limits move the entire speed distribution towards lower speeds, but for measures like speed cameras and ISA, the speed distribution is changes most for higher speeds. In the third study, where different models that study accident risk and speed levels are compared, it is shown that models developed to estimate an individual driver's risk give an unreasonable impact on risk change compared to aggregate models such as the power model. An alternative approach to take into account a change in the speed distribution is to use the power model at an individual level. The greatest difference is obtained for higher severity injuries and measures such as speed cameras and ISA where the speed distribution changes its shape the most.

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