With the growing legalization of marijuana use in states across the country, concerns have persisted over its effects on drivers of all kinds of vehicles.
A new study shows that this effect might be even worse than was originally thought because drivers seem to be unable to tell how impaired they are.
One problem is that drivers under the influence of cannabis are often unaware of the negative impact it has on their judgment and reflexes at different times after ingesting the drug, according to experiments conducted by researchers at the University of California-San Diego.
Cannabis users displayed significantly diminished ability on a Composite Drive Score that assessed key simulated driving variables, such as swerving in lane, responding to divided attention tasks and attempting to follow a lead car.
However, not all of those drivers displayed significantly diminished driving skills compared to a separate group that injested a non-THC placebo. Only about 50% of users could be described as “impaired,” which could complicate matters for law enforcement if the experiment’s results are replicated by other researchers.
The comparative decline in performance was sharpest at the 30- and 90-minute marks after inhaling cannabis, leveled off to only borderline differences with the placebo group at 3 ½ hours, and showed no difference at 4 ½ hours.
Researcher Thomas Marcotte noted that, “although users in the THC group felt impaired and were hesitant to drive at 30 minutes, by 90 minutes they believed the impairment was wearing off and were more willing to drive.”
This may contribute to unsafe operations by inducing a false sense of safety, he added. “This was despite their performance not significantly improving from the 30 minute point. This may indicate a false sense of safety, and these first few hours may constitute a period of greatest risk since users are self-evaluating whether it is safe to drive.”