in this way a more exact picture of the developments is formed and the search for explanations is more focused a past decrease in crashes is no guarantee that crashes will decrease in the future only if there is a better understanding of the reasons for the decrease will it be possible to formulate expectations about future developments there are indicators for unsafe traffic behaviour eg speeding driving while intoxicated the safety quality of vehicles eg ncap stars the safety of roads eg international road assessment program irap stars and the quality of the trauma system eg arrival times of ambulances analysts can consider to what extent the execution of policies has influenced the spis and to what extent a change in spi has led to a change in the number of casualties