Explainers

Debunker: Major 'drugged driving' report's findings prove overblown

June 22, 2017
A simulated drugged driving traffic stop in California. Officials are overstating the danger of drugged driving compared to alcohol and cell phones.  (AP Photo/Rich Pedroncelli)
Rich Pedroncelli
A simulated drugged driving traffic stop in California. Officials are overstating the danger of drugged driving compared to alcohol and cell phones. (AP Photo/Rich Pedroncelli)
SOURCE: Rich Pedroncelli

Media coverage of a recent Governors Highway Safety Administration report suggests that marijuana-impaired drivers are becoming a road safety threat on par with drunk drivers.

But a closer inspection of the relevant data finds no support for these claims. The report's findings were so overblown, even Mother’s Against Drunken Driving protested its findings. Let’s dig in.

Specifically, the Governors report cites federal Fatality Analysis Reporting System (FARS) data, which report on the prevalence of drugs identified in fatal crash victims. An overview of this data finds an uptick in the percentage of drivers testing positive for traces of the main active ingredient in pot, THC, or its byproducts. But the FARS data possesses several important limitations:

  • For one thing, a significant portion of drivers (about a third) involved in fatal accidents are never tested for drugs or alcohol.
  • For another, data collection is inconsistent from state to state.
  • Most importantly, the data does not identify whether drug-positive drivers were either impaired at the time of the crash or culpable for the accident.
  • In fact, no uniform thresholds for drug-induced driver impairment even exist for any substance other than alcohol.

Nonetheless, the Governors’ report purports that drug-influenced drivers are overtaking drunken drivers as America’s primary traffic safety threat — an allegation so dubious that it motivated representatives from Mothers Against Drug Driving to publicly denounce the GHSA’s claims.

alcohol remains a greater contributor to crash risk than all other drugs combined

“There is no way you can say drugs have overtaken alcohol as the biggest killer on the highway,” J.T. Griffin, chief government affairs officer at MADD, responded. “The data is not anywhere close to being in a way that would suggest that.”

He’s correct. In fact, a 2014 review of US fatal traffic accident data by researchers at the Pacific Research Institute in Maryland reported definitively that alcohol remains a greater contributor to crash risk than all other drugs combined.

"Alcohol was not only found to be an important contributor to fatal crash risk, ... it was associated with fatal crash risk levels significantly higher than those for other drugs,” the study’s authors concluded. “The much higher crash risk of alcohol compared with that of other drugs suggests that in times of limited resources, efforts to curb drugged driving should not reduce our efforts to pass and implement effective alcohol-related laws and policies.”

As for marijuana’s potential role in traffic accidents, the PRI analysis reported, “Somewhat unexpected was the finding that although marijuana's crude OR (odds ratios) indicated a significant contribution to fatal crash risk, once it was adjusted by the presence of alcohol and drivers' demographics, marijuana's OR was no longer significant among either sober or drinking drivers.”

Road Safety Data Exonerates Marijuana

Their finding that marijuana appears to play little to no significant role in fatal accidents is hardly unique.

While some crash culpability studies report a slightly elevated risk of motor vehicle accident in THC-positive drivers compared to drug free drivers, others — including the largest US government-sponsored study of its kind — do not. Among those studies that do report a link, this elevated risk is typically well below the risk of accident associated with many other non-criminal behaviors, such as driving with two or more passengers (OR = 2.2) or operating a motor vehicle while pregnant (OR =1.42). It is also significantly lower than the risk of accident associated with driving after consuming alcohol within legal limits, which increases crash risk by as much as 400 percent, even after controlling for drivers’ age and gender. According to recently published case-control data in the journal Injury Epidemiology, drivers testing positive for alcohol possess an elevate risk of motor vehicle accident that is more than ten times higher than that of drivers who test positive for THC alone.

Most significantly, data from states that have liberalized marijuana’s legal status show no spike in motor vehicle crashes. Writing in December in the American Journal of Public Health, investigators at Columbia University reported, "[O]n average, medical marijuana law states had lower traffic fatality rates than non-MML states. .... Medical marijuana laws are associated with reductions in traffic fatalities, particularly pronounced among those aged 25 to 44 years. ... It is possible that this is related to lower alcohol-impaired driving behavior in MML-states.”

An assessment of traffic fatality data from Colorado yielded a similar conclusion, reporting, “… legalization is associated with a nearly nine percent decrease in traffic fatalities, most likely to due to its impact on alcohol consumption.” A recent Congressional Research Service report concluded, “… there was no trend identified in the percentage of drivers testing positive for marijuana (either marijuana only or marijuana in combination with other drugs/alcohol) for those involved in traffic fatalities and who were tested for drugs or alcohol” in Washington state post-legalization. A similar review of motor vehicle crash data in Oregon similarly reported regulating the adult marijuana market has not led to an increase in fatal accidents.

As for the reported uptick in the percentage of drivers testing positive for either THC or its metabolites, there are several explanations. One, states are far more routinely engaging in the toxicological testing of drivers now than in the past. Two, more adults are using marijuana today than were a decade ago. And three, both THC and its primary metabolite, carboxy-THC are detectable on a toxicological exam for extensive periods of time. (In regular consumers, THC may be present in blood for up to a week post-consumption, while carboxy-THC may be present in urine for several months.) In short, more Americans today may be getting stoned than in the past. But that doesn’t mean that there are more stoned drivers on the road.

Roadways Safer Than Ever

In fact, data from the US National Highway Traffic Safety Administration indicates that America’s roadways are safer than ever — despite recent legal and cultural shifts with regard to the use of cannabis. In 1996, NHTSA reports that there were an estimated 37,500 fatal car crashes on US roadways. But by 2014, during which time a majority of states legalized medical cannabis and several others passed laws either reducing or eliminating marijuana-related adult use penalties, this total fell to just under 30,000.

Nevertheless, common sense dictates that efforts should be made to better educate the public with regard to the existing traffic safety laws, as well as to how acute cannabis intoxication influences driving performance. In particular, this messaging should stress that cannabis may have greater effects on more naive users, and that combining marijuana and alcohol possesses an additive adverse effect on driving performance that is typically is associated with a far greater risk of accident as compared to the use pot alone. In addition to increasing public safety, implementing these steps will help to assuage concerns that regulating the adult use of marijuana could potentially lead to an increase drugged driving incidences or limit the state’s ability to identify and prosecute those who may pose a legitimate traffic safety threat while under its influence.

Paul Armentano is the Deputy Director of the National Organization for the Reform of Marijuana Laws (NORML) and is the co-author of the book Marijuana Is Safer: So Why Are We Driving People to Drink? (Chelsea Green Publishing, 2013).