• S Jongen, A Vermeeren, N N J J M van der Sluiszen, M B Schumacher, E L Theunissen, K P C Kuypers, E F P M Vuurman, and J G Ramaekers.
• Department of Neuropsychology and Psychopharmacology, Faculty of Psychology and Neuroscience, Maastricht University, Universiteitssingel 40, 6200 MD, Maastricht, The Netherlands. stefan.jongen@maastrichtuniversity.nl.
• Psychopharmacology (Berl.). 2017 Mar 1; 234 (5): 837-844.

IntroductionThe on-the-road highway driving test is generally regarded as a gold standard for assessing drug-induced driving impairment. The primary outcome measure is the standard deviation of lateral position (SDLP), a measure of road tracking error or "weaving". The test has been calibrated for incremental doses of alcohol almost 30 years ago in order to define the impact of drug-induced impairment in terms of blood alcohol concentration (BAC) equivalents. Drug-induced changes in SDLP exceeding 2.4 cm have been evaluated as clinically relevant ever since. The present analysis was conducted to assess the robustness of the alcohol effect in a range of on-the-road driving studies which have been conducted since the initial alcohol calibration study.MethodsThe present study pooled data of 182 participants from nine placebo-controlled crossover studies who performed the highway driving test, while their BAC was at or just below the legal limit for drivers (i.e., 0.5 g/L).ResultsOverall, mean SDLP increased with 2.5 cm (95% CI 2.0-2.9 cm). Equivalence testing showed that the clinical relevance criterion value of 2.4 cm fell well within the 95% CI in each individual study. Gender did not affect alcohol-induced changes in SDLP.DiscussionThese results demonstrate the robustness and validity of the clinical relevance criterion for SDLP as measured during on-the-road driving.

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