Decisive for police intervention were unsafe driving (swerving, hesitating, or going too slowly), driving at high speeds within city limits, driving through red lights or stop signs, and driving at night without lights. In 20 percent of cases, drivers caused a traffic accident. Suspicion of driving under the influence of drugs was mainly caused by impaired coordination of movements, bloodshot eyes, slurred speech, drowsiness, conspicuous behavior, and changed pupils. In most cases, police recorded more than two symptoms. In 94 percent of cases, police suspicions could be confirmed by toxicological urine analysis. 31 references and 1 figure