A federal marijuana impairment report has cast a shadow of doubt over the THC testing methods and regulations used by law enforcement officers in America, citing the inability to detect THC impairment from biological test samples and the worthlessness of establishing a “per se” limit to designate THC impairment in drivers.
The National Highway Traffic Safety Administration prepared the report as required by a section of the Fixing America’s Surface Transportation Act signed by former President Barack Obama while he was still in office.
According to the NHTSA report, “the consistent finding is that the level of THC in the blood and the degree of impairment do not appear to be closely related.” This echoes the results of AAA’s study from last year.
Beyond blood tests, the NHTSA report found that a positive oral fluid test does not distinguish between personal marijuana use and environmental exposure and that positive tests for urine, sweat and hair do not count as evidence of THC impairment because they’re incapable of proving impairment at the time of driving.
Even though the level of THC in a user’s blood hasn’t been found to correspond with the degree of impairment, some states have enacted per se limits so that drivers who test above the state-legal THC limit can be charged with driving under the influence, whether or not they’re actually impaired.
The federal marijuana impairment report recommends improving detection and training methods so law enforcement officers can more accurately assess marijuana impairment as well as establishing an impairment standard for driving under the influence of marijuana.
The report also recommends encouraging states to collect relevant data on marijuana use by drivers and those arrested for impaired driving. The NHTSA previously collected such data, but a 2016 appropriations act prohibited the NHTSA from using FY 2016 funds to conduct roadside surveys on alcohol and drug use.