Q If cannabis use becomes more widespread, is an increase in traffic fatalities inevitable?

A There is no compelling evidence that cannabis contributes substantially to traffic accidents and fatalities. At some doses cannabis affects perceptions and psychomotor performance - changes which could impair driving ability. However, in driving studies, cannabis produces little car handling impairment - consistently less than that produced by low to moderate doses of alcohol and many legal medications. In contrast to alcohol, which tends to increase risky driving practices, cannabis tends to make subjects more cautious. Epidemiological surveys in Canada, Australia and the United States of drivers in fatal road accidents have found cannabis in the blood of 3- 11 per cent of dead drivers. However, in 70-90 per cent of these cases, alcohol was detected too. It is likely, however, that cannabis does contribute to bad driving in some individuals, especially inexperienced cannabis users and inexperienced drivers.

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