The principle aim of DRUID is to achieve knowledge about the different factors that influence driving under the influence of psychoactive substances (DUI) in order to combat DUI. Within this main objective several tasks are embedded in order to address different aspects of the problem. A rather important aim within WP 1 (research and methodology) is task 1.3, recommendation of thresholds for psychoactive substances in traffic. Setting a concentration threshold for a psychoactive substance in traffic means to presume that a driver above this threshold is likely unfit to drive and may be punished without further evidence. With respect to this consequence, it becomes immediately evident that on the one hand the decision for a concentration limit must be based on empirical results about the impairing potential but on the other hand cannot be restricted to those empirical results alone. Especially in case of psychoactive substances, the behavioral variance between persons is extremely high. Therefore, the relation between substance concentration and behavioral impairment (consequently driving fitness) will only be a probabilistic one. The higher a concentration limit is, the more likely impairment can be assumed for all drivers. As a consequence, the result of empirical studies – either epidemiological or experimental ones – is only one part of the discussion about reasonable concentration limits, albeit an important one. To justify a limit, other questions must be answered like: How precise concentrations can be measured? How large is the deterrence effect of per se limits? Is the accepted risk for medicament-induced impairment the same as for illicit drugs? Therefore, this compilation and discussion of empirical results about substance-induced impairment will only yield a framework for the much broader discussion about setting concentration limits. (Author/publisher) This document is available at https://www.bast.de/Druid/EN/Home/home_node.html
Samenvatting