Daily cannabis users are able to drive as safely as sober people, but less experienced stoners have a harder time driving under the influence, according to a recent study.
Researchers from the University of Colorado, Anschutz Medical Campus and the University of Iowa recruited 85 subjects between the ages of 25 to 45 to participate in their new study on cannabis and driving safety. Out of the total group, 31 subjects reported daily cannabis use, 24 reported smoking once or twice a week, and 30 did not get high at all. The researchers tested each participant to determine the THC levels in their blood at the time of the experiment.
At the start of the experiment, each subject completed a test drive and four brief driving scenarios in a driving simulator. After this, regular and occasional cannabis users were asked to smoke as much bud as they wanted for up to 15 minutes. Because of federal prohibition laws, subjects had to bring their own weed, but researchers asked subjects to bring flower with 15 to 30 percent THC content.
A half hour after blazing, researchers had the subjects participate in several distracted driving experiments. In these experiments, subjects were distracted from driving by an audio message asking them to select an app on a tablet mounted in the simulator. This task forced subjects to take their eyes off the road for about five seconds. During this time, the simulator recorded data about whether subjects drifted out of their lane, changed their speed, or showed any other signs of unsafe driving.
The study, which was recently published in the Traffic Injury Prevention journal, reports that the occasional pot smokers were more likely to veer out of their lane than regular stoners or sober subjects. “The results provide evidence that a pattern of occasional use was associated with performing worse after acute cannabis smoking as it relates to lane departures,” the researchers wrote, according to NORML. The daily cannabis users stayed in lane just as well as sober drivers, however.
Regular stoners also drove at consistently slower speeds than occasional users or sober drivers. “This would be consistent with the hypothesis of tolerance, with individuals with daily use being somewhat less affected by or better able to mitigate the effects of acute cannabis smoking,” the study authors explained. “This may indicate that those who use daily may perceive a potential adverse impact of acute cannabis use on driving performance and may attempt to compensate by slowing down to have more time to react to changes in the roadway.”
The study confirms the findings of a related study published in the Accident Analysis and Prevention journal last year. This study also reported that daily cannabis users were able to drive as safely under the influence as sober drivers, but occasional users performed significantly worse on the tests after getting high. Several other studies have also confirmed that regular cannabis users often drive slower than sober people, again suggesting that they are able to accurately compensate for any intoxicating effects.
The present study also confirmed prior research concerning the validity of THC tests for evaluating driving performance. All subjects abstained from cannabis for 12 hours before the experiment, but daily cannabis users still tested positive for THC despite being completely sober. Previous studies have found that sober subjects who smoked weed recently may test positive for THC on a drug test, but are still able to drive as safely as those who abstain from pot completely.
These studies confirm that THC tests cannot accurately predict whether or not a person is too stoned to drive safely. Advocacy groups are urging law enforcement to switch to performance tests or to adopt new technology rather than relying on these completely inaccurate testing methods.