Drugs and driving: when science and policy don't mix.

This commentary briefly looks at the Canadian federal government's proposed legislation to strengthen the enforcement of drug-impaired driving, placing special emphasis on cannabis. After outlining the legislation, three issues are examined. Of primary concern is at what level cannabis use impairs driving ability leading to an increased risk of motor vehicle collision. Current epidemiological evidence is reviewed. Equally important is the government's emphasis on the training and implementation of Drug Recognition Experts (DREs), specially trained police officers whose role is to detect drivers under the influence of drugs. Research on the effectiveness of DREs is discussed, along with a dialogue regarding the potential shortcomings of the DRE program. Finally, a brief surveillance of international policy literature on drugs and driving is offered, along with some sober thoughts on the potential difficulties that may emerge in the enforcement of the proposed legislation.