When states look to regulating marijuana, detractors – particularly in law enforcement – often warn about the difficulty in identifying and apprehending impaired drivers in the field and the potential for increased incidents of injury or death on the highway.
With little research to draw concrete ties between marijuana use and driver impairment, law enforcement has long argued their lack of ability to test for THC intoxication in the field has made marijuana laws difficult to enforce due to the lack of any real mechanism to prove a person driving a vehicle was, in-fact, impaired by marijuana.
To-date, most arguments by law enforcement have been anecdotal. However, a recent study appears to support those claims, concluding methods for testing alcohol levels in suspects, like field sobriety tests, were unreliable indicators of a person’s THC levels, i.e. how much marijuana is in their system at the time of the alleged infraction.
The study – backed by the National Institute of Justice, a research arm of the US Justice Department – concluded many perceived enforcement methods, like checking one’s THC levels in biofluids (such as blood, saliva, urine) are insufficient when it comes to proving someone’s motor skills were — or were not — impaired by marijuana use.
“THC levels in biofluid were not reliable indicators of marijuana intoxication,” a DOJ summary of the study concludes. “Many of their study participants had significantly decreased cognitive and psychomotor functioning even when their blood, urine, and oral fluid contained low levels of THC. The researchers also observed that standardized field sobriety tests commonly used to detect driving under the influence of drugs or alcohol were not effective in detecting marijuana intoxication.”
The DOJ study’s results underscore the complexities in evaluating the impacts of a psychoactive substance from person-to-person, along with the unique nature of evaluating those impacts to determine whether criminal charges should – or even could – be issued based on one’s THC levels.
Further complicating the study’s conclusions and its implications for law enforcement is a lack of a close and demonstrated relationship between marijuana use and a person’s ability to drive. However, it’s not for a lack of trying.
Opponents of legalized marijuana have long-argued its use significantly impairs the speed of one’s mental and physical capabilities, according to a 2018 report to Congress by the National Highway and Traffic Safety Administration. Numerous studies cited by the National Institute on Drug Abuse in their own talking points have found a direct relationship between blood THC concentration and impaired driving ability.
Next to alcohol, marijuana is also one of the top substances most frequently found in the blood of persons involved in car crashes: according to a recent Colorado Department of Transportation study on the topic, 13.5% of drivers involved in fatal crashes in 2018 tested positive for cannabis, well-above a 2013 baseline of 10% and below a 2016 high of 20% according to a 2017 analysis by the Denver Post. To counter the trend, the Colorado DOT has rolled out a statewide public awareness campaign to reduce instances when individuals choose to drive under the influence.
In a 2019 research review published by the Missouri Journal of Medicine, David Evans – a former coordinator for the New Jersey Intoxicated Driving Program and an attorney whose work centers around “victims of the marijuana industry” – argued legalization could lead to “mayhem” on Missouri’s highways, citing data from Colorado and Washington state.
However, the truth is much more complicated. Researchers who evaluated traffic death incidents in Colorado and Washington “observed that recreational cannabis laws were associated with increases in traffic fatalities in Colorado but not in Washington state, [perhaps due to] the size of the marijuana industry in Colorado, evidence of cannabis tourism in Colorado and other local aspects,” one of the study’s co-authors, Julian Santaella-Tenorio, told UPI.
Another article published by the American Bar Association on 4/20 last year presented similar arguments, stating that while statistics and reporting on impaired driving from state to state were “sporadic,” the data available did point to the conclusion that legalization have led to increases in traffic incidents resulting in injury or death.
However, the author concluded too little was known or understood about the drug and its connection to those incidents to define any concrete policy from his findings.
“We see already the increased complexity in impaired-driving cases, and trial delays occasioned by unavailability of witnesses and significant backlogs in state and local drug testing laboratories,” the author, ABA fellow and Maryland District Court Judge Neil E. Axel, wrote in the piece. “Perhaps we are now experiencing some of the unknown consequences of legislative enactments that occur faster than the development of science.”