Unlike alcohol, it's difficult to designate a legal limit of weed for a person who's driving, a new study reports. At a time when marijuana continues to be legalized in the U.S., and other places such as Jamaica, the study could help shape the laws currently in place for when someone gets caught for a marijuana DUI.
According toArs Technica, a study done by the AAA Foundation for Traffic Safety says testing a person's bloodstream for THC levels (like one would test for the .08 legal limit of blood alcohol concentration) can't help determine how high is too high for a person to get behind the wheel.
AAA researchers looked at the toxicology tests results of drivers who had been arrested for impaired driving and results of Drug Recognition Expert (DRE) exams, which includes field sobriety tests. Researchers found people with low levels of THC in the bloodstream can still act really high, but also that people with high levels of THC can still act normal.
Researchers saw sober people, 349 of them to be exact, did better on the DRE exam in comparison to how the 602 drivers with THC in their blood did on the DRE exam. The DRE exam included a walk-and-turn test that 55.5 percent of the sober people pass in comparison to the 6 percent of marijuana users who passed.
The performance of the 602 marijuana using drivers did not correlate with their THC levels, which the study reports ranged from 1 to 47 nanograms per milliliter of blood. Higher levels of THC did not mean a less successful performance.
Researchers compared the results of impaired drivers with the 5 ng/mL legal THC limit in Colorado, Washington, and Montana. According to the study, of the drivers under the influence of marijuana who failed the sobriety tests, 80 percent had a 1 ng/mL or higher THC level. However, 30 percent of those who passed also had a 1 ng/mL THC level.
As Ars Technicawrites, other factors play a major role beside THC level—including how much weed is used and how frequent smokers may have higher THC levels for longer periods.
Thus, researchers concluded marijuana limits are "arbitrary and unsupported by science, which could result in unsafe motorists going free and others being wrongfully convicted for impaired driving."
