All too often, it’s not just drivers behind the wheel, but alcohol and cannabis too. A new report shows there’s a clear pattern of increased crash risk associated with amphetamine, benzodiazepines, and opioids.  -  Photo: Canva

All too often, it’s not just drivers behind the wheel, but alcohol and cannabis too. A new report shows there’s a clear pattern of increased crash risk associated with amphetamine, benzodiazepines, and opioids.

Photo: Canva

A new safety research report from the National Transportation Safety Board (NTSB) found that between 71% and 99% of drivers in five populations studied tested positive for one or more potentially impairing drugs.

Nearly one in three traffic fatalities in the United States involve alcohol-impaired driving, and driving while impaired by other drugs alone or combined together, also continues to be a major hazard on the nation’s roadways. The NTSB’s new safety research report examines the crash risk associated with different drugs, including alcohol, and the prevalence of their use among drivers.

The report is dense, and the findings are based on multiple study endeavors. For example, NTSB conducted an extensive literature review, which found that multiple drugs and drug categories — like stimulants or sedatives — are associated with impaired performance and increased crash risk. In addition, the researchers evaluated drug data in national-level databases, but confirmed that it continues to be unreliable and cannot be used to estimate drug prevalence among drivers.

To counter that problem, the NTSB analyzed the best available toxicological data from five populations of drivers, including drivers arrested for impaired driving and fatally injured drivers, from the Orange County, California, Crime Laboratory; the Wisconsin State Laboratory of Hygiene, which provided data for two populations of drivers; the New York State Police Forensic Investigation Center; and the San Francisco Office of the Chief Medical Examiner.

The findings are worrisome. As noted, between 71% and 99% of drivers in the five populations studied tested positive for one or more potentially impairing drugs. What's more, about 50% of drivers tested positive for more than one category of drug.

Alcohol and cannabis were the two most commonly detected drugs across all populations studied. While alcohol was most often detected alone, cannabis was most often detected in combination with alcohol or other drugs.

“We’ve long known about the devastating impact of alcohol-impaired driving, but this report shows that impairment from other drugs, especially cannabis, is a growing concern that needs to be addressed,” said Tom Chapman, NTSB member. 

Although a primary focus was given to alcohol and cannabis due to their documented prevalence, numerous other drugs, including illicit, prescription, and over the counter (OTC) drugs, were also examined.

The researchers concluded that alcohol continues to be the drug with the most detrimental impact on traffic safety. Nonetheless, cannabis and other potentially impairing drugs contribute to the problem of impaired driving crashes.

Impaired Driving Prevalence, Trends

Beginning in the 1980s, there was a substantial reduction in both the number of impaired driving fatalities and the fatality rate, notes the report. However, since 2010 there has been little change, except in 2020, when there was a notable increase, which coincided with the COVID-19 pandemic. The National Transportation Safety Administration (NHTSA) estimated that 11,654 people died in crashes involving an alcohol-impaired driver in 2020 alone.

The prevalence of other drug use beyond alcohol is more difficult to determine due to inconsistencies in the collection and testing for drugs. Therefore, tracing crash trends that link back to drug-impaired drivers is not easy or reliable.

However, despite the limitations of national fatal crash data concerning other drug use and driving, there are major societal trends in drug prescribing and drug use over the past two decades that may have affected the prevalence of drug use among drivers and drug-related crashes. This includes a significant increase in prescription drug use — including potentially impairing benzodiazepines, muscle relaxants, and opioid analgesics — among adults of all ages in the U.S.

There has also been a general movement to legalize recreational cannabis use over the past decade. Since 2012, some 21 states, the District of Columbia, and two U.S. territories have legalized recreational cannabis use, according to the report. Research about the effects of such measures on the prevalence of cannabis use among the driving population and traffic safety have shown mixed results.

But beyond societal trends, several surveys indicate that people admit to using drugs while driving.

The National Survey on Drug Use and Health, an annual survey conducted by the Substance Abuse and Mental Health Services Administration, found that, in 2020, more than 1 in 10 respondents reported driving under the influence of alcohol and/or an illicit drug(s) in the past year. The two most-reported drugs were alcohol at 7.2% and cannabis at 4.5%. About 1% of respondents reported driving under the influence of other selected illicit drugs, including cocaine, heroin, hallucinogens, inhalants, and methamphetamine.

Moreover, a nationally representative survey of drivers conducted by the AAA Foundation for Traffic Safety in 2020 found that 5.9% admitted to driving when they were over the alcohol limit in the past month, 4.4% admitted to driving within an hour of using marijuana, and 3.4% admitted to driving when using potentially impairing prescription drugs. 

Alcohol, Drugs, and Crash Risk

The report explores how individual drugs and drug categories impact on crash risk. The results from multiple studies described in the report suggest that several drugs or drug categories are associated with significantly increased crash risk or increased likelihood of responsibility in a multivehicle crash.

There was a clear pattern of significantly increased risk associated with alcohol, amphetamine, benzodiazepines, and opioids. For several other drugs and drug categories, one or more meta-analyses indicated increased risk for certain types of crashes.

The report also addresses drug combinations and their impact on crash risk. The research challenges for understanding the effects of a single drug are greatly multiplied when examining drug combinations. There are nearly unlimited combinations of drugs that may each affect a given driver differently.

For example, the DRUID project compared drug presence from crash-involved drivers (cases) to non-crash-involved drivers (controls) to assess the crash risks of individual drugs as well as the risks associated with combining alcohol with other drugs and multiple drug use that did not include alcohol.

The aggregated results showed that the odds of drivers being seriously injured in a crash, compared to drivers who tested negative for drugs, were more than 28 times higher for drivers who tested positive for alcohol combined with other drugs and 8 times higher for drivers who tested positive for more than one non-alcohol drug.

The report explores several more studies that examine crash risk associated with drivers who have used a combination of drugs as well as specific categories of drugs.

Testing and Countermeasures

The NTSB report also highlights that current testing practices and protocols need to be improved to both better detect a driver’s drug use and accurately report the prevalence of drug-impaired driving.

For example, many jurisdictions halt testing when a driver’s blood alcohol concentration is over a certain threshold, losing valuable information on other drugs the driver may have used. Additionally, a lack of standardized drug testing and reporting hinders understanding of the issue and the development of policies that can reduce impaired driving, as well as treatment options for those with substance abuse disorders. 

However, testing is only a part of the solution. NTSB says stakeholders must also work on laws, enforcement, education, and treatment interventions. It also discusses very specific countermeasures to reduce impairment-related crashes.

Multiple Stakeholders, Recommendations

The report concludes with several NTSB recommendations aimed at state and federal agencies, and is essentially an urgent call-to-action to all stakeholders.

“Impaired driving leads to tragedy every day on our nation’s roads, but it doesn’t have to,” said NTSB Chair Jennifer Homendy in a press statement. “To create a truly safe system — one where impaired driving is a relic of the past — states and federal agencies must implement our recommendations, and fast. Further complacency is inexcusable.” 

Some of the recommendations to states include, for example, a requirement that cannabis products have a warning label about driving impairment; enhancements to state drug-impaired driving laws; and modification of laws to allow for oral fluid collection, screening, and testing for the detection of drug use by drivers.

In its report, the NTSB also specifically calls upon NHTSA to disseminate a common standard of practice to state officials for drug toxicology testing as well as establish a program to support toxicology laboratories’ compliance with a standard practice for the toxicological testing of biological specimens.

In addition, NTSB recommends that NHTSA establish a trauma center-based sentinel surveillance system. In other words, a collection of reporting sites that provide timely and high-quality data to measure trends in the prevalence of drug use among crash-involved drivers.

Finally, NTSB issued three recommendations to the US Food and Drug Administration (FDA). These include conduct a study to understand how drug labels could be modified to increase user understanding and compliance with driving-related warnings and publish the study findings.

The NTSB also suggests the FDA develop a system to audit drugmaker compliance with FDA guidance to evaluate drug effects on the user’s ability to operate a motor vehicle. Lastly, NTSB recommends incorporating additional data and research concerning drug use and driving to improve FDA drug safety surveillance systems.

About the author
Marianne Matthews

Marianne Matthews


Marianne Matthews contributes safety news and articles for the Fleet Safety newsletter. She is an experienced trade editor.

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