New Study Finds ‘No Support’ For Fear That Marijuana Legalization Normalizes Impaired Driving
From toxifillers.com with love
Contrary to concerns among some critics that legalizing marijuana would normalize cannabis-impaired driving, a new study found “no support that marijuana legalization increased tolerant behaviors and attitudes toward driving after marijuana use.”
The report, authored by researchers at Nationwide Children’s Hospital and Ohio State University and published late last month in Biometrical Journal, used data from national traffic safety survey and compared responses from Kentucky and Tennessee—where medical marijuana was illegal during the study period—against responses from eight other states where medical cannabis was already legal.
“The concern that legalizing marijuana will affect traffic safety is prevalent in both academic and political discourse,” the study says, contending that the relationship “can be tested using causal interference methods that estimate treatment effects on those in states who have yet to legalize medical marijuana.”
“However,” authors added, “answering this causal question with survey data requires novel analytical techniques.”
Authors looked at responses to four questions in the Traffic Safety Culture Index (TSCI), a national survey conducted by the AAA Foundation for Traffic Safety. The questions asked about whether people had driven within an hour of marijuana use, how personally acceptable they found driving after marijuana use (what researchers referred to as “DAMU”), how they felt consumption affected one’s driving ability and whether they viewed drugged driving as a threat to their personal safety.
Using a matched-pairs design, the analysis matched responses from Kentucky or Tennessee with responses from legal medical marijuana states on a one-to-one basis—an effort to control for other variations between people filling out the survey and isolate the variable of cannabis’s legal status. That data was then used to model any potential effects of the policy change in Kentucky and Tennessee.
“We rooted our study in the idea that medical marijuana legalization would cause residents would exhibit greater tolerance toward DAMU,” wrote the three-author research team. “We found practically no evidence for this hypothesis, and our conclusions were unlikely to change due to the moderate level of unmeasured confounding.”
Though the team described the statistical findings of the analysis as robust, they acknowledged that limitations in methodology could affect the reliability of the findings. For one, they noted that the responses were self-reported and may not be wholly accurate. Data was also limited to only a single year, 2017, in which all four relevant cannabis-related questions were included on the TSCI survey.
The study also attempted to predict the effects of legalization in only two Southern states, the report says, noting that the findings “may not generalize to other states that have yet to legalize medical marijuana.” Further, authors said they could have limited their pool of legal medical marijuana states to only those immediately neighboring Kentucky and Tennessee, which may have better controlled for cultural differences between populations.
Despite drugged driving frequently arising in policy discussion around marijuana reform, Americans more broadly say they’re more concerned about other risky practices, such as using a cell phone, driving drunk, going too fast or driving aggressively. That’s according to a Pew Research Center poll released last month.
The survey, which looked at public opinion on traffic concerns, found a majority of Americans (82 percent) still regard driving while high on cannabis to be either a major problem (37 percent) or minor problem (45 percent) in their area. But respondents ranked it lowest among six behaviors included in the survey.
For example, 96 percent of respondents said they considered driving while distracted by cellphones a problematic issue in their community. Another 94 percent said speeding was a problem, while 93 percent said aggressive driving behaviors such as a tailgating was a concern.
Ninety-two percent identified drunk driving as a problem where they live.
A recent study by Canada’s public health agency, Health Canada, meanwhile, found that self-reported rates of driving after cannabis use fell in the years following nationwide legalization. Specifically, 18 percent of people who reported using cannabis within the past year also said they’d driven afterward, which officials described as “a significant decline from 27% in 2019.”
A separate scientific review recently concluded that most available research on cannabis-impaired driving identified “no significant linear correlations between blood THC and measures of driving,” although there was an observed relationship between levels of the cannabinoid and reduced performance in some more complex driving situations.
In a separate report earlier this year, the National Highway Traffic Safety Administration (NHTSA) said there’s “relatively little research” backing the idea that THC concentration in the blood can be used to determine impairment, calling into question laws in several states that set “per se” limits for cannabinoid metabolites.
Similarly, a Department of Justice (DOJ) researcher said in February that states may need to “get away from that idea” that marijuana impairment can be tested based on the concentration of THC in a person’s system.
“If you have chronic users versus infrequent users, they have very different concentrations correlated to different effects,” Frances Scott, a physical scientist at the National Institute of Justice (NIJ) Office of Investigative and Forensic Sciences under DOJ, said.
That issue was also examined in a recent federally funded study 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.
Back in 2022, Sen. John Hickenlooper (D-CO) sent a letter to the Department of Transportation (DOT) and NHTSA seeking an update on the status of a federal report into testing THC-impaired drivers. The department was required to complete the report under a large-scale infrastructure bill that President Joe Biden (D) signed, but it missed that deadline and is unclear how much longer it will take.
Last summer, a 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 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.
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