The issue of marijuana-impaired driving arose again at congressional hearing last week, with a representative of the Governors Highway Safety Association emphasizing the importance of roadside drug testing as a tool to help combat deadly car crashes.
“I think the first and foremost thing that is going to assist us in preventing those tragedies from taking place is oral fluid roadside testing,” said Michael Hanson, who’s also director of traffic safety at the Minnesota Department of Public Safety.
Hanson was responding to a question from House Transportation & Infrastructure Subcommittee on Highways and Transit member Rep. Rob Bresnahan (R-PA), who had asked how to address concerns around impaired driving.
“With states getting out in front of federal legislation relating to marijuana specifically,” he said, “do you have any recommendations or ideas or technologies that we can start to implement that would detect a more instantaneous level of impairment?”
In response, Hanson pointed to saliva testing as an example of “instruments and technology” that law enforcement officers could deploy in the field “to detect recent use of a cannabis product that is a strong indicator that that person may be impaired.”
“Putting those tools in the hands of law enforcement to prevent that from happening—or allow them to process somebody who may be impaired—is going to be important,” he told lawmakers at the February 12 hearing.
Written testimony from Catherine Chase, president of Advocates for Highway and Auto Safety, also pointed to measures such as “extending zero tolerance for under age 21 and open container laws to include marijuana use and its products”—laws already on the books in most states with legal cannabis.
With more than three quarters of all U.S. states having legalized marijuana for either medical or adult use, and in light of the possibility of federal rescheduling of the drug, concerns about highway safety loom large before policymakers. Though there’s no widely agreed-upon way to test impairment by drivers at a roadside stop, efforts to develop and deploy field tests that screen for recent use have become more urgent in recent years.
The National Institute of Standards and Technology (NIST), for instance, is planning to convene government officials, forensics experts, academics, industry representatives, law enforcement and standards organizations in April for what it describes as “an open and candid discussion” about “the path forward to realize meaningful cannabis breathalyzer technology and implementation.”
Topics to be discussed will include challenges facing marijuana breathalyzer design and development, obstacles to prosecutors handling drugged-driving cases and how NIST and others might partner to advance the technology.
Impaired driving is of particular concern to the trucking industry, which has raised worries that rescheduling marijuana could complicate zero-tolerance drug policies.
Bresnahan at a separate congressional hearing last month asked Cargo Transporters Inc. CEO Dennis Dellinger, who was testifying on behalf of the American Trucking Associations (ATA), whether there was “anything specifically that Congress can do, or advocate for, to detect that immediate level of impairment with the half-lives of marijuana remaining inside of systems.”
Dellinger replied that he thinks “there’s a misconception out there, [with] marijuana or cannabis being legal, that people can operate vehicles under the influence, and that is a problem.”
“We do not have a test that tells us if you are under the influence or not, so we have to rely on the current urine test or the hair test, which tests back [beyond active impairment],” he said. “And I guess the struggle we have in our industry is we can’t compromise the system we have until there is a workable solution for a test to know whether you are actually under the influence at the time.”
“I think, in our company, if we had an accident at any degree, and we had post-accident tests and we tested positive, we would struggle defending anything in that accident,” Dellinger continued. “And the retribution we would get for that from the public, from the media, would be astonishing. So our position is that, right now, we have to accept the testing that we have.”
In 2023, the U.S. Department of Transportation (DOT) finalized a rule permitting another alternative option to screening urine samples: saliva-based testing. Depending on frequency of use, THC is generally detectable in saliva anywhere from one to 24 hours after use, according to the agency.
While saliva or blood tests can detect recent marijuana use better than urine or hair samples, however, there’s another wrinkle: According to recent comments by a U.S. Department of Justice (DOJ) researcher, it’s unclear whether a person’s THC levels are even a reliable indicator of impairment.
On a podcast last year, Frances Scott, a physical scientist at the National Institute of Justice (NIJ) Office of Investigative and Forensic Sciences under DOJ, questioned the efficacy of setting “per se” THC limits for driving. Ultimately, she said, there may not be a way to assess impairment from THC levels, as law enforcement does for alcohol.
One complication is that “if you have chronic users versus infrequent users, they have very different concentrations correlated to different effects,” Scott said. “So the same effect level, if you will, will be correlated with a very different concentration of THC in the blood of a chronic user versus an infrequent user.”
Last October, a study preprint posted on The Lancet by an eight-author team representing Canada’s Centre for Addiction and Mental Health, Health Canada and Thomas Jefferson University in Philadelphia identified and assessed a dozen peer-reviewed studies measuring “the strength of the linear relationship between driving outcomes and blood THC” published through September 2023.
“The consensus is that there is no linear relationship of blood THC to driving,” the paper concluded. “This is surprising given that blood THC is used to detect cannabis-impaired driving.”
Most states where cannabis is legal measure THC intoxication by whether or not someone’s blood THC levels are below a certain cutoff. The study’s findings suggest that relying on blood levels alone may not accurately reflect whether someone’s driving is impaired.
“Of the 12 papers included in the present review,” authors wrote, “ten found no correlation between blood THC and any measure of driving, including [standard deviation of lateral position (SDLP)], speed, car following, reaction time, or overall driving performance. The two papers that did find a significant association were from the same study and found significant relationship with blood THC and SDLP, speed and following distance.”
The issue was also examined in a federally funded study last year that identified two different methods of more accurately testing for recent THC use that accounts for the fact that metabolites of the cannabinoid can stay present in a person’s system for weeks or months after consumption.
A 2023 congressional report for a Transportation, Housing and Urban Development, and Related Agencies (THUD) bill said that the House Appropriations Committee “continues to support the development of an objective standard to measure marijuana impairment and a related field sobriety test to ensure highway safety.”
A year earlier Sen. John Hickenlooper (D) of Colorado sent a letter to the Department of Transportation (DOT) seeking an update on that status of a federal report into research barriers that are inhibiting the development of a standardized test for marijuana impairment on the roads. The department was required to complete the report under a large-scale infrastructure bill that President Joe Biden signed, but it missed its reporting deadline.
Meanwhile, National Transportation Safety Board (NTSB) last year warned that marijuana rescheduling could create a “blind spot” with respect to drug testing of federally regulated workers in safety-sensitive positions—despite assurances from then-U.S. Transportation Secretary Pete Buttigieg that the cannabis rescheduling proposal “would not alter” the federal drug testing requirements.
At a House committee hearing, Buttigieg had referenced concerns from ATA “about the broad public health and safety consequences of reclassification on the national highway system and its users,” which the trucking association voiced in a letter to the secretary.
As more states legalize marijuana, a federal report published last year showed that the number of positive drug tests among commercial drivers fell in 2023 compared to the year before, dropping from 57,597 in 2022 to 54,464 in the prior year. At the same time, however, the number of drivers who refused to be screened at all also increased by 39 percent.
Another question found that 65.4 percent of motor carriers believed current marijuana testing procedures should be replaced with methods that measure active impairment.
At the time, the report from the American Transportation Research Institute (ATRI) noted a 65,000-driver deficit in the country and said the fear of positives over marijuana metabolites—which can remain in a person’s blood far long after active impairment—may be keeping would-be drivers out of the industry.
The record-high number of refusals came as the transportation industry faces a nationwide shortage of drivers, which some trade groups have said has only been made worse by drug testing policies that risk flagging drivers even when they’re not impaired on the job.
Current federal law mandates that commercial drivers abstain from cannabis, subjecting them to various forms of drug screening, from pre-employment to randomized testing.
In June 2022, meanwhile, an ATRI survey of licensed U.S. truck drivers found that 72.4 percent supported “loosening” cannabis laws and testing policies. Another 66.5 percent said that marijuana should be federally legalized.
Cannabis reform advocates, meanwhile, have also called on federal officials to change what they call “discriminatory” drug testing practices around the trucking industry.
A top Wells Fargo analyst said in 2022 that there’s one main reason for rising costs and worker shortages in the transportation sector: federal marijuana criminalization and resulting drug testing mandates that persist even as more states enact legalization.
Then-Rep. Earl Blumenauer (D-OR) sent a letter to the head of DOT in 2022, emphasizing that the agency’s policies on drug testing truckers and other commercial drivers for marijuana are unnecessarily costing people their jobs and contributing to supply chain issues.
The 2022 ATRI report noted that research into the impact of cannabis use on driving and highway safety is currently mixed, complicating rulemaking to address the issue. A separate 2019 report from the Congressional Research Service (CRS) similarly found that evidence about cannabis’s ability to impair driving is inconclusive.
A study published in 2019 concluded that those who drive at the legal THC limit—which is typically between two to five nanograms of THC per milliliter of blood—were not statistically more likely to be involved in an accident compared to people who haven’t used marijuana.
Separately, the Congressional Research Service in 2019 determined that while “marijuana consumption can affect a person’s response times and motor performance … studies of the impact of marijuana consumption on a driver’s risk of being involved in a crash have produced conflicting results, with some studies finding little or no increased risk of a crash from marijuana usage.”
Another study from 2022 found that smoking CBD-rich marijuana had “no significant impact” on driving ability, despite the fact that all study participants exceeded the per se limit for THC in their blood.
Evan as far back as 2015, a U.S. National Highway Traffic Safety Administration (NHTSA) concluded that it’s “difficult to establish a relationship between a person’s THC blood or plasma concentration and performance impairing effects,” adding that “it is inadvisable to try and predict effects based on blood THC concentrations alone.”
In a separate report last year, NHTSA said there’s “relatively little research” backing the idea that THC concentration in the blood can be used to determine impairment, again calling into question laws in several states that set “per se” limits for cannabinoid metabolites.
“Several states have determined legal per se definitions of cannabis impairment, but relatively little research supports their relationship to crash risk,” that report said. “Unlike the research consensus that establishes a clear correlation between [blood alcohol content] and crash risk, drug concentration in blood does not correlate to driving impairment.”
Supreme Court Asked To Settle Differing Interpretations Of Federal Medical Marijuana Protections Amid Lower Court Discrepancy
Photo courtesy of Chris Wallis // Side Pocket Images.
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