Blood samples collected from 2500 non-fatally injured drivers involved in road crashes were analysed for the presence of alcohol, cannabinoids, benzodiazepines and stimulants. Evaluation of the causal role of the drug in the crash was based on culpability analyses using data collected at the crash scene. A total of 22.6 percent of drivers tested positive for at least one drug including alcohol. Either alone or in combination with other drugs, alcohol was found in 12.4 percent of drivers, cannabinoids in 10.8 percent, benzodiazepines in 2.7 percent and stimulants in 1.3 percent. A small number of cannabinoid-positive drivers tested positive for tetrahydrocannabinol (THC, the main active ingredient in marijuana) while most drivers tested positive for the inactive metabolite. While benzodiazepine concentrations were at levels consistent with therapeutic use, the types of stimulants used and their concentrations suggested mainly illicit use of these drugs. A clear causal role was found for alcohol, with increased culpability rates at high blood alcohol concentrations. When those with very low concentrations were excluded, benzodiazepines use was also associated with higher culpability. Consistent with earlier research, cannabinoids were not found to be associated with increased culpability. Relatively few drivers tested positive for stimulants and there was no clear evidence of greater culpability. Overall, alcohol plays the greatest role in road crashes, but benzodiazepines also have a significant effect. (a) For the covering entry of this conference, please see ITRD abstract no. E202275.
Abstract