By Lauren Smith
Updated: 22 May 2023 & medically reviewed by Dr. Kimberly Langdon
More than half (56%) of individuals killed or seriously injured in car accidents in the United States have drugs and/or alcohol in their system, with 20% testing positive for two or more substances, a new major study conducted by the National Highway Traffic Safety Administration (NHTSA) has found.
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More than half of drivers were impaired
And many were seriously intoxicated: nearly one-fifth (19.9%) of the drivers were found to have blood alcohol levels (BAC) above 0.08%, exceeding the legal drunk driving limit in every state.
Additionally, 14.2% of all drivers tested, and 26.1% of those who were killed, had BACs above 0.15%, a level at which motor control deteriorates and vision blurs and doubles.
“The use of multiple substances at once can magnify the impairing effects of each drug,” said Acting NHTSA Administrator Ann Carlson.
Impairment of all road users
The research also considered other killed or injured road users, including car passengers, bicyclists, pedestrians, and those on other vehicles such as mopeds, all-terrain vehicles (ATVs), and electric kick scooters.
Of all patients, 25.1% tested positive for THC, the psychoactive ingredient in cannabis, while 23.1% had alcohol in their bloodstream. 10.8% had used stimulants, and 9.3% were under the influence of opioids.
One in five was under the influence of more than one substance. The presence of two or more substances was detected in 18% of cases with serious injuries and 32% of cases with deaths.
The high rate of detected cannabis may reflect the increasing acceptance of the drug and its legalization for recreational use in 21 states. However, it also stays in the bloodstream longer than alcohol or other drugs, said Amy Berning, a research psychologist at the NHTSA and an author of the study.
Data collected at trauma centers and medical examiner offices
The study drew on blood samples from car accident victims at seven Level 1 trauma centers, in Miami and Jacksonville, Florida; Charlotte, North Carolina; Baltimore; Worcester, Massachusetts; Iowa City, Iowa; and Sacramento, California. Medical examiners at four sites also participated, testing patients who died at the scene of the accident.
The blood samples collected were screened for the presence of substances known to potentially impair driving and general road use, including alcohol, cannabinoids, stimulants, sedatives, opioids, and antidepressants.
Ultimately, data was gathered on 7,279 road users who were killed or seriously injured in these locations between the autumn of 2019 and the summer of 2021.
This was a critical time on the country’s roads, as the pandemic encouraged reckless driving and contributed to seven straight quarterly increases in traffic deaths from the summer of 2020.
The results were “scary to all of us,” said Michael Brooks, executive director of the nonprofit Center for Auto Safety. But they weren’t a surprise, he added.
“There’s not a commute that goes by that I don’t smell marijuana on the road, from someone actively smoking in a car in front of me,” he said, describing his experience in Washington D.C. Recreational cannabis is legal in the nation’s capital city and became legal in the adjoining state of Virginia in July 2021.
Berning noted that the study doesn't prove a connection between rising numbers of serious accidents and the growing prevalence of drug use and wasn’t nationally representative. However, the detection of such a high rate of impairment among road users is “a concern for NHTSA,” she said.
The agency, part of the Department of Transportation, will use this data as a baseline for further study, she said. The agency is also planning on conducting a national roadside survey to measure alcohol and drug use among road users, the first it’s conducted since 2013-14.