Impaired Driving

Key points

  • Impaired driving happens when someone operates a vehicle while impaired by substances such as marijuana, illicit drugs, prescription drugs, over-the-counter medicines, and/or alcohol.
  • Driving while impaired by any substance is dangerous and illegal.
  • There are effective measures that can help prevent injuries and deaths from impaired driving.
A guy refusing an alcohol drink while holding car keys.

Effects of substances on driving

Safe driving requires focus, coordination, good judgment, and quick reactions to the environment. Any alcohol or other drug use impairs the ability to drive safely.

The amount of alcohol in a person's system can be measured. This measurement is called blood alcohol concentration (BAC). Most states have set the legal BAC limit for driving at 0.08 grams of alcohol per deciliter (g/dL); the limit is 0.05 g/dL in Utah.1 However, impairment starts at lower BAC levels. Information on the effects of alcohol on driving at a range of BACs is available here.

We know a lot about alcohol's effects on driving, but more research is needed to fully understand the impact of drugs on driving skills.2 However, research has shown that both legal and illicit drugs impair the skills needed to drive safely. For example:

  • Some of the effects of being impaired by marijuana that can affect driving include slowed reaction time and decision making, impaired coordination, and distorted perception.2345
  • Other drugs (such as cocaine or illicit amphetamines) can also impair skills like perception, memory, and attention in the short or long term.2
  • Prescription and over-the-counter medications can cause many side effects that can impact driving, such as sleepiness, impaired vision, and impaired coordination.6
  • Use of multiple substances (such as marijuana and alcohol) at the same time can increase impairment.57

Impacts

In 2020, 11,654 people were killed in motor vehicle crashes involving alcohol-impaired drivers, accounting for 30% of all traffic-related deaths in the United States.8

32 people in the United States are killed every day in crashes involving an alcohol-impaired driver — this is one death every 45 minutes.8

It is not known how many people are killed each year in crashes involving drug-impaired drivers because of data limitations.9 Regardless, driving while impaired by any substance is dangerous and illegal.

Keep Reading: Impaired Driving Facts

People at increased risk

Some groups are more at risk for impaired driving and related crashes and deaths. These include teen drivers and passengers,10 young adult drivers, men, and drivers who don't always wear a seat belt.8

Keep Reading: People at Increased Risk for Impaired Driving

What the research shows

There are multiple effective measures that states and communities can take to prevent alcohol-impaired driving. These include actively implementing and enforcing lower BAC limits11 and implementing sobriety checkpoints. 12

Keep Reading: Preventing Impaired Driving

What you can do

For drivers: Plan ahead. If you plan to drink alcohol or use drugs, make plans so that you do not have to drive.

For everyone: Don't let your friends drive while impaired by alcohol and/or drugs. If you're hosting a party where alcohol or drugs will be available, remind your guests to plan ahead.

Keep Reading: What You Can Do to Prevent Impaired Driving

Resources

Drug-impaired driving fact sheet

The drug-impaired driving fact sheet provides an overview of drug-impaired driving. This fact sheet highlights strategies that states can use to address drug-impaired driving and identifies actions that can be taken.

Additional resources

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Content Source:
National Center for Injury Prevention and Control
  1. Insurance Institute for Highway Safety (IIHS), Highway Loss Data Institute (HLDI). Alcohol and Drugs. Insurance Institute for Highway Safety, Highway Loss Data Institute; 2022.
  2. Busardo FP, Pichini S, Pellegrini M, Montana A, Lo Faro AF, Zaami S, Graziano S. Correlation between Blood and Oral Fluid Psychoactive Drug Concentrations and Cognitive Impairment in Driving under the Influence of Drugs. Curr Neuropharmacol. 2018;16(1):84–96. doi:10.2174/1570159X15666170828162057
  3. National Academies of Sciences, Engineering, and Medicine; Health and Medicine Division; Board on Population Health and Public Health Practice; Committee on the Health Effects of Marijuana: An Evidence Review and Research Agenda. The Health Effects of Cannabis and Cannabinoids: The Current State of Evidence and Recommendations for Research. Washington, DC: National Academies Press (US); 2017.
  4. Compton R. Marijuana-Impaired Driving – A Report to Congress (Report No. DOT HS 812 440) [PDF – 44 pages]. Washington, DC: U.S. Department of Transportation, National Highway Traffic Safety Administration (NHTSA); July 2017.
  5. Hartman RL, Huestis MA. Cannabis effects on driving skills. Clin Chem. 2013;59(3):478–492. doi:10.1373/clinchem.2012.194381
  6. Centers for Disease Control and Prevention (CDC). Medicines Risk Fact Sheet. U.S. Department of Health and Human Services, Centers for Disease Control and Prevention. 2020.
  7. Lacey JH, Kelley-Baker T, Berning A, Romano E, Ramirez A, Yao J, Compton R. Drug and alcohol crash risk: A case-control study (Report No. DOT HS 812 355) [PDF – 190 pages]. Washington, DC: U.S. Department of Transportation, National Highway Traffic Safety Administration; December 2016.
  8. National Highway Traffic Safety Administration (NHTSA). Traffic Safety Facts 2020 Data: Alcohol-Impaired Driving (Report No DOT HS 813 294). Washington, DC: U.S. Department of Transportation, National Highway Traffic Safety Administration, National Center for Statistics and Analysis; April 2022.
  9. Berning A, Smither D. Traffic Safety Facts Research Note: Understanding the Limitations of Drug Test Information, Reporting, and Testing Practices in Fatal Crashes (DOT HS 812 072). Washington, DC: U.S. Department of Transportation, National Highway Traffic Safety Administration (NHTSA), National Center for Statistics and Analysis. April 2022.
  10. Voas RB, Torres P, Romano E, Lacey JH. Alcohol-related risk of driver fatalities: an update using 2007 data. J Stud Alcohol Drugs. 2012;73(3):341–350. doi:10.15288/jsad.2012.73.341
  11. National Academies of Sciences, Engineering, and Medicine; Health and Medicine Division; Board on Population Health and Public Health Practice; Committee on Accelerating Progress to Reduce Alcohol-Impaired Driving Fatalities. Getting to Zero Alcohol-Impaired Driving Fatalities: A Comprehensive Approach to a Persistent Problem. Negussie Y, Geller A, Teutsch SM, editors. Washington, DC: National Academies Press(US); 2018.
  12. Venkatraman V, Richard CM, Magee K, Johnson K. Countermeasures That Work: A Highway Safety Countermeasures Guide for State Highway Safety Offices, 10th Edition, 2020 (Report No. DOT HS 813 097) [PDF – 641 pages]. Washington, DC: U.S. Department of Transportation, National Highway Traffic Safety Administration (NHTSA); July 2021.