Two U.S. House committees briefly addressed the issue of marijuana-impaired driving as part of broader transportation-related hearings last week. During testimony, a representative of the trucking industry called for wider use of hair follicle drug testing, while the chair of the National Transportation Safety Board (NTSB) recommended better education for drivers.
While no formal action was taken by the panels, the exchanges highlight the ongoing frustration from lawmakers, regulators and the commercial trucking industry, among others, around the lack of available methods to reliably test drivers for marijuana impairment despite state-level legalization and possible federal rescheduling of the drug.
First, at a hearing of the House Appropriations Subcommittee on Transportation, Housing and Urban Development on Wednesday that centered on congressional oversight of the National Transportation Safety Board (NTSB), Rep. David Joyce (R-OH)—a co-chair of the Congressional Cannabis Caucus—asked NTSB Chair Jennifer Homendy what federal and state governments could do to address drug-impaired driving.
“Though 34 states have changed their laws regarding legal marijuana, it’s still illegal everywhere to drive while intoxicated,” he began, referencing a 2022 NTSB report that found testing protocols needed to be improved.
“The lack of standardized drug testing and reporting hinders understanding of the issue and development of policies that can reduce impair driving as well as treatment options for those with substance abuse disorders,” Joyce continued. “We need to be doing more research especially in the development of tools that help identify the presence of drugs in drivers.”
He then asked Homendy: “What does the NTSB recommend other federal agencies and state governments do to address the rise in drug-impaired driving accidents, especially as more communities across the U.S. are beginning to legalize recreational marijuana and be subjected to this?”
Homendy didn’t specifically mention drug testing in her response to Joyce’s question. Rather, she pointed to what she described as a widespread lack of education around cannabis and driving.
“I’m sure you all remember that when we all went to school, we had driver education as part of our school curriculum. It was pretty robust,” she replied. “Today, that education doesn’t occur.”
Pointing to a fatal drug-impaired accident in Oklahoma, she said NTSB “found that driver education around drug-impaired driving did not occur. Now, they put that back in place, but that doesn’t occur across our country.”
She asserted that a large subset of drivers may not even know it’s illegal to drive under the influence of THC.
“Organizations have done some research and have found that for teen drivers in particular…a third of them think it is legal to drive after intaking marijuana. Twenty-five percent of adults,” Homendy said.
“Usage has gone up significantly,” she continued, “and we need to do a number of things, including testing protocols, training for law enforcement officers so they can detect drug-impaired driving, increased enforcement and then training itself for the public.”
Joyce, for his part, said he “wholeheartedly” agreed with Homendy’s assessment. He then pivoted to expressing concern about the availability of unregulated intoxicating hemp products.
“What’s even more disturbing is the crap that they sell at local gas stations to underage kids without any regulation that creates much worse effects,” the lawmaker said, ostensibly referring to hemp products that were legalized through the 2018 U.S. Farm Bill.
Homendy responded that she’s the parent of a 17-year-old, “and I worry about it all the time.”
“We’ve all been at traffic lights in D.C. where somebody pulls up and you can smell it,” she said. “It’s awful, and, uh, terrible tragedies that we have investigated over and over again involving marijuana, other drugs and then alcohol, of course.”
“Thank you very much for your work,” Joyce concluded.
Joyce is one of two Republican co-chairs of the Congressional Cannabis Caucus, which installed new Democratic leadership at the beginning of the new year. As of earlier this month, however, members had yet to hold an initial meeting.
Later Wednesday, at a hearing of the House Transportation and Infrastructure Subcommittee on Highways and Transit, a trucking industry representative expressed frustration at current drug-testing protocols for commercial drivers.
John Elliott, executive chairman of Michigan-based logistics company Load One, testified on behalf of the Truckload Carriers Association, of which he’s a past chairman. He said Congress should take action to make hair follicle drug testing an alternative to urine testing, noting that it has a longer detection window (up to 90 days) and is “more challenging to manipulate.”
Some motor carriers already use hair follicle testing under their own policies, but Elliott noted that positive tests are unable to be added to U.S. Department of Transportation (DOT) Drug and Alcohol Clearinghouse, “allowing these drivers to work immediately for other carriers when only using urine testing.”
“At time when conversations lean towards the potential reclassification of marijuana from a Schedule I to Schedule III narcotic, demonstrating that this problem is likely to only grow,” he said, “our industry in its entirety is unable to properly employ the proper test to identify habitual users and enter them into a substance abuse program and begin the return-of-duty procedures.”
Further into the hearing, Rep. David Rouzer (R-NC), subcommittee chair, asked Elliott, “How big a problem is marijuana use in terms of supply of drivers?”
“I think it’s unfortunately going to be a bigger and bigger problem as more states move to legalize and classify it,” Elliott replied. “Again, I think it comes back to testing. I don’t think we want anyone behind the wheel who’s impaired. We lack current technology comparable to a breathalyzer.”
Rep. Mike Bost (R-IL) also queried Elliott about drug testing.
“It’s not just the trucking industry, it’s heavy equipment, it’s pilots,” he said. “Alcohol, we do have a way…a breathalyzer test. The marijuana situation is, you smoke one joint and you’re going to be popping positive [on a urine test] for 30 days.”
“We don’t have a way to keep it controlled and safe because we don’t have the proper testing,” Bost added. “Can you expand on that issue, as well, please?”
“The only tool we have right now that’s better than what we have is hair follicle testing,” Elliott replied. “We’re allowed to use it, on one hand, but we’re hiding the results from our own industry and from the public and from the federal government. And we need to remove that roadblock as quickly as possible if we want to make the road safer.”
In written testimony, a representative for the International Brotherhood of Teamsters spoke out against federal adoption of hair follicle standards for drug testing.
The union asserted that when the U.S. Department of Health and Human Services (HHS) last tried to set guidelines for hair testing, the effort “failed so spectacularly to address core concerns…that stakeholders across the board expressed grave concerns about the viability of the proposal.”
Beyond hair follicle testing, another alternative to urine tests is saliva-based screening, which did not appear to be mentioned during the subcommittee hearing.
DOT finalized new testing policies in 2023 to allow oral saliva drug testing as an alternative to urine-based tests. This past December, however, critics lamented that more than a year and a half after finalizing the rule, federal officials had yet to set up the infrastructure necessary to allow the new testing procedure to be used.
Oral fluid testing is more easily observable without the same privacy concerns as urine tests. Some advocates saliva testing say that it also better determines impairment because it detects recent marijuana use, thus reducing false positives in situations such as post-accident drug tests.
The potential for false positives is what Bost was referring to in his comment about “popping positives for 30 days” after a single joint.
By contrast, hair follicle testing could increase false positives by detecting marijuana use months before a test is administered.
Written testimony from Lewie Pugh, executive vice president of the Owner-Operator Independent Drivers Association, said there are “still significant debates and unanswered questions concerning the use of hair testing.”
“We do know hair testing can lead to false positives because of contamination from the environment and the interference of cosmetic treatment on the analysis of hair,” his comments said. “Variances in hair types have also posed difficulties in standardizing drug testing. Hair shape, size, color, texture, formation, and other qualities varies by race, sex, age, and position on the scalp. Not surprisingly, all these limitations have led to discriminatory employment practices.”
Pugh said those concerns were behind HHS’s decision to refrain from adding hair testing to its proposed guidelines in 2020.
Outside the Capitol, a Substance Abuse and Mental Health Services Administration (SAMHSA) official recently downplayed criticism from the CEO of a drug-testing company that more widespread use of saliva-based drug testing “means truckers who use cannabis will be able to do so with near impunity, as long as they avoid a drug test for a couple of days.”
“When a donor receives a request for collection, the donor will not know if the test will be an oral fluid or urine collection until they arrive at the collection facility for a federal agency,” the unidentified SAMHSA official said in response. Not knowing whether to expect a saliva or urine test, in other words, would prevent drivers simply stopping marijuana use a few days before a saliva-based test.
Another federal agency—the National Institute of Standards and Technology (NIST)—had been planning an event for next month to convene government officials, forensics experts, academics, industry representatives, law enforcement and standards organizations for what it described as “an open and candid discussion” about “the path forward to realize meaningful cannabis breathalyzer technology and implementation.”
A NIST official recently told Marijuana Moment, however, that the workshop had been “postponed until the summer, date TBD,” providing no further details.
Topics to be discussed at the event are meant to include challenges facing marijuana breathalyzer design and development, obstacles to prosecutors handling drugged-driving cases and how NIST and other entities might partner to advance the technology.
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.
Impaired driving is of particular concern to the trucking industry, which has raised worries that rescheduling marijuana could complicate zero-tolerance drug policies.
Last month, the issue of marijuana-impaired driving arose congressional hearing, 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.
Responding to a question from House Transportation & Infrastructure Subcommittee on Highways and Transit member Rep. Rob Bresnahan (R-PA), Hanson also 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.
The transportation industry also advised Congress in January that if marijuana is federally rescheduled, businesses want assurances that they won’t have to forgo zero-tolerance drug policies for drivers—while stressing that a key problem for the sector is a lack of technology to detect impaired driving.
While saliva and blood tests can detect recent marijuana use better than urine or hair samples, there’s another wrinkle: As recently acknowledged 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 signed by President Joe Biden, 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.”
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