Methods for testing impairment of driving due to drugs

The Transport and Road Research Laboratory has been concerned for a long time with possible causes of driving difficulties and has developed methods for investigating driving performance. The question addressed here was how applicable these methods are in assessing driving problems arising from the use of drugs which can impair performance, particularly widely-available centrally-acting drugs. We assessed four types of driving-related tests by comparing their sensitivities with two laboratory tests, developed elsewhere, which measure more basic effects of drugs on performance, using drugs known to impair skills. Performances under the influences of ethanol, the benzodiazepine lorazepam, and the antihistamine triprolidine, each given both as a single high dose and a single low dose, were compared with performances after placebo. We used double-blind crossover design, in which subject variability was minimized by studying only women of a limited age range (45-55 y). The driving-related tests detected the effects of the substances used, although they were generally less sensitive than the laboratory tests. The individual sensitivities of the driving test could be improved to match those used for more general assessments.