Does Marijuana Impair Driving?
It is against the law to drive while under the influence of marijuana. It has always been assumed that cannabis, like alcohol, impairs the perception, coordination, reflexes and judgment necessary for the safe operation of a motor vehicle. And, of course, there have been governmental studies addressing the question: Does marijuana impair driving?
Interestingly, however, the findings do not necessarily support popular opinion.
On the one hand, the California Department of Justice has found that marijuana undoubtedly impairs psychomotor abilities that are functionally related to driving and that driving skills may be impaired, particularly at high-dose levels or among inexperienced users. “Marijuana and Alcohol: A Driver Performance Study”, California Office of Traffic Safety Project No. 087902 (Sept. 1986).
Contradicting these conclusions, however, are two federal studies. The U.S. Department of Transportation conducted research with a fully interactive simulator on the effects of alcohol and marijuana, alone and in combination, on driver-controlled behavior and performance. Although alcohol was found consistently and significantly to cause impairment, marijuana had only an occasional effect. Also, there was little evidence of interaction between alcohol and marijuana. Accidents and speeding tickets reliably increased with alcohol, but no marijuana or combined alcohol-marijuana influence was noted.
However, the Ontario DUI statute makes it illegal to be in control of a motor vehicle while any amount of illegal drug is in your system. It is the drugs presence within the body that completes the crime of DUI, not being under the particular drugs influence at the time. Therefore, anyone who drives with an illegal drug in their system commits a DUI. This includes cannabis. Impairment is not relevant. A misdemeanor driving under the influence charge is eligible to be upgraded to a felony under a handful of circumstances. A DUI that results in causing great bodily harm or death to another is one of those circumstances.
The Supreme Court ruled that the defendant was properly found guilty of Aggravated DUI because his negligence was a proximate cause of the accident that resulted in death, and because he had an illegal drug in his system at the time. In particular, the Supreme Court ruled that impairment does not need to be a proximate cause of the accident or injuries. It did not matter that the drug was methamphetamine. Marijuana use would have resulted in the same ruling.
A more recent report entitled “Marijuana and Actual Performance”, noted that “THC is not a profoundly impairing drug….It apparently affects controlled information processing in a variety of laboratory tests, but not to the extent which is beyond the individual’s ability to control when he is motivated and permitted to do so in driving”.