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Fed’s Stoned Driving Study Is Most Comprehensive Ever

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NADS dome interior with updated projection and graphics. Image courtesy of University of Iowa NADS, photo by Omar Ahmad

NADS dome interior with updated projection and graphics. Image courtesy of University of Iowa NADS, photo by Omar Ahmad

The U.S. government recently completed a study in which participants got stoned on marijuana, or on a combination of marijuana and alcohol, and then got behind the wheel of a driving simulator, according to news reports. As reports, the scientists who worked on the study say it is the most comprehensive ever done on how marijuana affects drivers.

The federally funded simulator, NADS — the University of Iowa’s National Advanced Driving Simulator — is located in Iowa City, where researchers recruited volunteers. “They were happy to participate,” says Dr. Marilyn Huestis, chief of chemistry and drug metabolism at the Intramural Research Program at the National Institute on Drug Abuse, KHOU writes.

In the study, each of the 19 volunteers was required to drive on the simulator after consuming specific amounts of marijuana, marijuana and alcohol, or a placebo, KHOU writes. To consume the pot, the volunteers had to use a vaporizer, because the university has a smoke-free campus.

The marijuana used in the study came from a “federal garden” at the University of Mississippi, KHOU writes. Matt Ferner writes for Huffington Post that it is the federal government’s only sanctioned marijuana farm.

Huestis said the experiment took three years for researchers to design and conduct. The tests were completed this spring and the data are expected to be available by October, KHOU writes.

Ferner writes of the volunteers, who were all between the ages of 21 and 55:

Subjects in the simulator sat in a complete car and ‘drove’ as a 360-degree realistic world was projected on the domed walls around them. Researchers at the NADS had previously developed programs to test the distractive effects of texting and cell phone use, and the sedative effects of alcohol, but Huestis and University of Iowa engineers had to specifically design environments for the cannabis driving test, since it was the first of its kind.

The simulator put the volunteers through many different driving situations, Ferner writes. They included an urban section with crowds and lights, a highway section, and a rural section. The drivers had to deal with such situations as deer coming onto the road, people entering a crosswalk, signs telling drivers to turn, and cars approaching and passing, Ferner writes.

KHOU interviewed Colorado State Trooper J.J. Wolff, whom it describes as one of the state’s top experts in identifying impaired drivers. Wolff said that he has not seen more stoned drivers since the state legalized recreational pot at the start of this year.

Colorado law says that “a driver is presumed to be too impaired to drive if his or her THC-blood level is higher than five nanograms of active THC per milliliter of blood, although the driver can rebut that charge and possibly overturn it in court,” Ferner writes. Huestis tells Ferner that five nanograms per milliliter might be too permissive a standard:

‘Many occasional users who are not chronic, frequent users can be very intoxicated at one nanogram per milliliter of blood and should not be driving.’

She said it will take more than a year for the researchers to analyze the more than 200 parameters from the study and announce their conclusions, Ferner writes.

In an editorial titled “The Great Colorado Weed Experiment,” Lawrence Downes writes in The New York Times that Colorado is expanding the number of specially trained “drug recognition expert” law enforcement officers to 300 in an effort to keep stoned drivers off the roads:

Research on the dangers of mixing marijuana and driving is scant, but so is evidence that legal cannabis makes the highways more dangerous.

Finally, in an article in Bustle, Alicia Lu offers “some humble suggestions” law enforcement could consider in trying to identify stoned drivers. Here are two of them:

  • Suspect is driving with one hand while shoving massive amounts of junk food into their mouth with the other.
  • Suspect is listening to Bob Marley, Willie Nelson, or Snoop Dogg.


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