NHTSA Studies Find Drugged Driving Increasing, but Drunk Driving Poses Bigger Crash Risk

NHTSA Studies Find Drugged Driving Increasing, but Drunk Driving Poses Bigger Crash Risk
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February 17, 2015

A study from a federal agency found that while drunk driving has declined, drivers with detectable levels of marijuana and prescription drugs in their system is increasing. Despite the increase, a companion study found that those drivers are at a lower risk of getting into an accident than drunk drivers.

The National Highway Traffic Safety Administration (NHTSA) earlier this month released two studies; one, a roadside survey of alcohol and drug use and the other, which assessed the crash risk of marijuana users.

Since the Roadside Survey of Alcohol and Drug Use by Drivers was first conducted in 1973, the number of drivers with alcohol in their system has declined by nearly three-quarters. Since 2007, the number has dropped by one-third. The same survey, however, found a large increase in the number of drivers using marijuana or other illegal drugs. In 2014, about one in four drivers tested positive for at least one drug.

The roadside survey is gathers data from drivers at 300 checkpoints throughout the country. Drivers are notified using street signage that a checkpoint is in the area and can stop if they wish. About 85 percent of drivers who pulled into the checkpoints chose to provide breath samples, more than 70 percent provided oral fluid, and over 40 percent chose to provide blood samples. The collected data was anonymous and drivers were compensated up to $60 for their time.

Conducted in Virginia Beach, Va., the second survey gathered data during a 20-month period from more than 3,000 drivers who were involved in crashes, as well as a comparison group of 6,000 drivers who were not.

The study found that drivers who had been drinking above the 0.08 percent legal limit had about 4 times the risk of crashing as sober drivers and those with blood alcohol levels at 0.15 percent or higher had 12 times the risk.

But, drivers participating in the study were tested for a larger number of potentially impairing drugs using both saliva and blood samples. Drivers testing positive for marijuana were overrepresented in the crash-involved population, but when demographic factors and alcohol use were control, the study did not find an increase in crash risk associated with marijuana use.

Marijuana is absorbed in the body differently than alcohol, which means detectable levels of the drug could be still be found in a user's body fluids days, weeks or months later, well after the impairing effects have worn off.

"Drivers should never get behind the wheel impaired, and we know that marijuana impairs judgment, reaction times and awareness," Jeff Michael, NHTSA's associate administrator for research and program development, said in a statement. "These findings highlight the importance of research to better understand how marijuana use affects drivers so states and communities can craft the best safety policies."