The properties of Safety Performance Indicators in target setting, projections and safety design of the road transport system.

Road traffic Safety Performance Indicators (SPIs) are becoming increasingly used as an instrument for the planning and monitoring of safety progress. SPIs form an intermediate step between actions and final outcome in terms of casualties in road crashes. It is understood that SPIs are closely related to outcome; and that it is also possible to use them in calculations and predictions of both actions and final outcome. In the present study, it was found that some of the properties assigned to SPIs could be questioned. An assumption of linearity between SPIs and final outcome was partly rejected. It was also found that 100% fulfillment of a set of SPIs could lead to very low mortality, demonstrating the importance of handling SPIs simultaneously.