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Study Finds Stoned Drivers More Likely to Crash

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Driving stoned on marijuana; courtesy National Institute on Drug Abuse

Driving stoned on marijuana; image courtesy National Institute on Drug Abuse

A study recently released by the U.S. Department of Transportation’s National Highway Traffic Safety Administration finds that marijuana users are more likely to be involved in traffic accidents. However, the reasons are complex, according to an NHTSA press release:

[T]he increased risk may be due in part because marijuana users are more likely to be in groups at higher risk of crashes. In particular, marijuana users are more likely to be young men – a group already at high risk.

The 20-month-long study, which NHTSA says is “the most precisely controlled study of its kind,” was conducted in Virginia Beach, Va., and gathered data from more than 3,000 drivers who were involved in car accidents, plus a comparison group of 6,000 drivers who were not in accidents. Although researchers tested drivers for “a large number of potentially impairing drugs using both oral fluid (saliva) and blood samples,” marijuana (THC) was the only category of drug that produced study findings that were statistically significant, the study’s executive summary says. The summary reports:

About 66 percent of the case subjects were involved in property-damage-only crashes and 33 percent were involved in injury crashes. Less than 1 percent of case subjects were involved in fatal crashes.

Strengths of this study design include the large number of case and control subjects, careful matching of case and control samples, and consistent protocols for alcohol and drug testing. Limitations of the study include a crash distribution biased toward less severe events. Findings based a sample of more severe crashes may differ. The study could not control for factors that could affect impairment by THC such the amount ingested, the potency ingested, prior experience with THC, and individual differences in response to THC.

Although the risks of driving while under the influence of alcohol have been known for decades, a lot less is known about how drug use affects driving, the Drug and Alcohol Crash Risk study says. “In the United States, recent State actions to legalize the use of marijuana for medical and recreational use have further exacerbated concern over potential risks of driving impaired by marijuana,” the study reports.

As Thor Bensen writes for UPI, the study also found that although drunk driving continues to be a problem, its incidence has decreased in recent years. Benson quotes Jeff Michael, NHTSA’s associate administrator for research and program development, as saying, “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.”

NHTSA plans on conducting a series of additional studies to better understand the risks of drugged driving, the NHTSA press release says. That will include the Washington State Roadside Survey (to assess the risks in one state where recreational marijuana use is legal), and a simulator study with the National Institute on Drug Abuse to provide information on the behavior of drivers under the influence of drugs, the release says.

The four states that have legalized the recreational use of marijuana include Colorado, which celebrated the one-year anniversary of its legalization on January 1; Washington, which legalized recreational pot on June 1 of last year; and Oregon and Alaska, whose legalization laws will go into effect in 2016, as Chris Boyette and Jacque Wilson write for CNN. In addition, 27 states and the District of Columbia have legalized medical marijuana or decriminalized its possession, CNN notes.

CDOT drugged driving campaign imageColorado’s Department of Transportation provides campaign materials to deter drugged driving. It is illegal in Colorado to consume marijuana while driving on any public road, as CDOT states on its website. Colorado law says that drivers with five nanograms of active THC (the psychoactive element in marijuana) in their “whole blood” can be prosecuted for DUI. However, no matter the level of THC, law enforcement officers base arrests on observed impairment,” CDOT writes.


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