“I’ve got friends who say that if you’ve smoked cannabis you’re likely to be a better driver because you’re going to be cautious and drive more slowly. Is that true?”
While the effects of alcohol on driving are well-known and have been widely studied, the effects of cannabis on driving are less clear and continue to be debated. Extensive research has established an alcohol level above which there is impairment and increased crash risk (in Australia, authorities have deemed that to be 0.05 for full licence holders, 0.00 for L- and P-platers), similar levels have not been agreed for cannabis, i.e., we don’t have an equivalent BAC for THC.
It’s often suggested that, unlike drunk drivers, those who smoke cannabis are more aware of their intoxication and, as a result, take precautions when getting behind the wheel of a car after using the drug, such as driving more slowly and carefully. While this may reduce some of the risks involved with driving ‘stoned’, research suggests there’s still a significant safety issue mainly due to cannabis-affected drivers having a slower reaction time and alertness.
Cannabis use has been found to affect a range of skills necessary for driving such as attention, hand-eye co-ordination, time and distance perception, decision-making and concentration. Most of these effects increase in a dose-dependent way, i.e., the more stoned you are, the greater the effect. Occasional smokers appear to be even more at risk. In addition, simulator and driving studies have shown that important driving skills such as steering, speed control, lane positioning and headway control (working out the distance between your car and the one in front of you) can all be affected after using cannabis.
Therefore, if a cannabis-affected driver is in a high-risk or unexpected situation (e.g., someone suddenly steps out in front of their vehicle), they’ll be less able to make an accurate judgement of the situation and may take longer to react, placing them at much greater risk of an accident.
Most people who choose to use drugs usually do so because they want ‘to change where they’re at’ – they want to have fun, feel more relaxed, or see, hear or think things in a different way. The one place you don’t want your perception to be changed is when you’re driving. If something was to go wrong and you hurt yourself, your friends or someone else because you’d smoked cannabis beforehand you’d never forgive yourself.
First published: October 2024
