Safe Transportation Research & Education Center

The use of cannabis, prescription drugs, and other drugs are increasingly prominent on roadways in the United States,where 25.3 percent of the nation’s 38,824 fatalities in 2020 were related to drug-involved driving. Driving can beimpaired by a variety of legal and illegal drugs, substances, and medications. The effect of specific drugs on behaviorand driving skills vary considerably depending on how they act in the brain and are metabolized. They can slow reactiontime, decrease coordination, increase aggressive and reckless driving, impair cognitive function, or cause drowsiness.All of these effects can contribute to crash risk.Studies suggest that poly-drug use or combining alcohol and drugs can inflate the level of driver impairment and crashrisk. There is variation across jurisdictions in the frequency of testing suspected impaired drivers for drugs, consistencyin laboratory drug testing practices, and capacity of law enforcement personnel. Despite challenges in identifyingcausality and impairment, there is general consensus that many drugs impair driving. Preliminary data from an ongoingNHTSA study of alcohol and drug prevalence during the COVID-19 emergency found some significant increases in theprevalence of drugs detected in blood among fatally and seriously injured drivers, motorcyclists, and pedestrians whencomparing the last quarter of 2019 and the first quarter of 2020 to the second, third, or fourth quarters of 2020. As ofFebruary 2022, nearly three-quarters of states, including California, have legalized medical-use of cannabis productsand over one-third allow recreational cannabis, increasing concerns about traffic safety. According to the NationalInstitute on Drug Abuse, aside from alcohol, cannabis is the most frequently detected drug in drivers who are in crashes.Analyses from FARS presented in the drug-impaired program area include fatalities in crashes that involved a driverwho tested positive for a drug that could cause impairment. Analyses from SWITRS presented in this program area referto drug-involvement and include fatal and serious injuries where law enforcement reported the driver to be under theinfluence of drugs. Crashes in the program area are defined as where one or more drivers tested positive for a drug thatcould cause impairment or was reported as driving under the influence of drugs, depending on which data set is used.