Driving under the influence

• 1. Introduction

  ›

  Driving under the influence, known by its initials DUI, is a crime that sits at the intersection of a simple human act and a complex legal web spanning every country on earth. On the 10th of September 1897, a London taxi cab driver named George Smith became the first person ever convicted of driving a motor vehicle while intoxicated. He was fined 20 shillings under the "drunk in charge" provision of the 1872 Licensing Act. That moment planted a seed. Over the following century, the offense would grow into one of the most prosecuted crimes in the world, under an alphabet soup of names, tested by science, fought over in courtrooms, and mourned in roadside memorials. What exactly counts as impaired? Who qualifies as a driver? And how does the world decide when a person behind the wheel has crossed the line?

• 2. A Crime With Many Names

  ›

  Across different legal systems, the same basic offense carries a startling number of labels. In the United States alone, states use terms including DUI, DWI, OWI, OVI, and "operating while ability impaired," each carrying its own legal nuance. Britain and Ireland favor "drink-driving." The UK also uses "drunk in charge" and "over the prescribed limit." Cannabis-specific offenses may be called "driving high" or "driving under the influence of drugs," abbreviated DUID.

  The variation in names reflects real variation in what the law actually prohibits. Most jurisdictions target anyone who drives while impaired, but the definition of "drive" matters more than it might seem. California requires actual movement of the vehicle before a DUI charge can stick. Most other US states go further, covering anyone who is physically in control of a motor vehicle while impaired, even if the car is parked. A person found sitting in the driver's seat, holding the keys, while intoxicated can face charges in those states without ever having moved.

  The legal reach extends well beyond cars and trucks. Many DUI statutes also cover motorcycling, boating, piloting aircraft, operating farm machinery such as tractors and combine harvesters, riding horses or driving horse-drawn vehicles, cycling, and skateboarding, sometimes with different blood alcohol thresholds than those that apply to ordinary driving. Washington state draws a specific distinction for cyclists. Its BUI law, bicycling under the influence, treats intoxicated cyclists as primarily a danger to themselves, so officers may impound the bicycle rather than file a formal DUI charge.

• 3. Alcohol's Toll

  ›

  In the United States, alcohol is involved in 30 percent of all traffic fatalities. Even a small increase in blood alcohol content measurably raises the relative risk of a crash. One study of drivers seriously injured in crashes found that 23.6 percent tested positive for alcohol, and 12.2 percent tested positive solely for alcohol with no other substance present.

  Despite those numbers, the full national picture for drug-impaired crashes remains incomplete. Data limitations mean that no national count exists for how many people die each year in crashes where drug impairment, separate from alcohol, is a factor. The same study that tracked alcohol found that 25.8 percent of seriously injured drivers tested positive for cannabinoids, 13.6 percent for cannabinoids alone, and 24.6 percent for a drug other than alcohol or cannabis.

  When a crash does occur and the driver is found to be impaired, the legal consequences extend beyond criminal charges. Car insurance for the intoxicated driver may be automatically declared invalid. In the American system, a DUI citation also triggers a major increase in insurance premiums going forward. Germany takes a different structural approach: its medical-psychological assessment program focuses on identifying unfit drivers and revoking licenses until fitness to drive can be re-established, with an interdisciplinary framework that also offers a path toward individual rehabilitation.

• 4. Testing Impairment

  ›

  Field sobriety tests are the first line of assessment when an officer suspects impairment. These are a battery of physical coordination tasks designed to establish probable cause for arrest in US jurisdictions. They are voluntary for most drivers, though some states require commercial drivers to accept preliminary breath tests.

  For suspected drug impairment beyond alcohol, law enforcement in the United States can call on the Drug Evaluation and Classification program, developed by the Los Angeles Police Department in the 1970s. The DEC program breaks detection into a twelve-step process carried out by a certified Drug Recognition Expert. Those steps run from a breath alcohol test and an interview with the arresting officer, through evaluation of the eyes, psychomotor tests, vital signs, a dark room examination, assessment of muscle tone, examination of injection sites, interrogation of the suspect, and the evaluator's formal opinion, finishing with a toxicological examination. DREs are qualified to testify in court as expert witnesses. The program is recognized by all fifty US states, Canada, and the United Kingdom, and the twelve-step process has been validated by both laboratory and field studies.

  Testing for cannabis impairment poses particular challenges. THC plasma levels decline significantly within one to two hours after a traffic stop, making timing critical. Several companies are developing roadside THC breathalyzers to give officers a faster tool. Some nations already use saliva swabs at the roadside, though questions about the reliability of saliva testing remain unresolved. Illinois law sets specific thresholds: a THC level of 5 nanograms or more per milliliter of whole blood, or 10 nanograms or more per milliliter of other bodily substances, triggers the prohibition. Even below those per se limits, an officer who believes a driver is impaired can still make an arrest.

• 5. Cannabis and Prescription Drugs

  ›

  A 2011 study published in the B.C. Medical Journal concluded that cannabis, like alcohol, impairs the psychomotor skills required for safe driving. The same study noted that cannabis-impaired drivers tend to drive more slowly and cautiously than drunk drivers, but that evidence still shows they are more likely to cause accidents than drug-free and alcohol-free drivers. A more recent 2023 study offered a different emphasis, finding that the impairment effect of marijuana on driving is relatively mild compared to alcohol, since drivers using cannabis drive slower, avoid overtaking other vehicles, and increase following distances.

  Colorado's approach reflects the ongoing difficulty of drawing a firm line. State law sets 5 nanograms of active THC in whole blood as the threshold at which prosecution for DUI becomes possible. At the same time, state policy makes clear that any amount of marijuana consumption puts a driver at risk of an impaired driving charge, and that officers base arrests on observed impairment regardless of the measured THC level. Colorado law also specifies that impairment is illegal even if the substance causing it was legally acquired or prescribed by a doctor.

  Prescription medications present a separate but related challenge. Opioids and benzodiazepines commonly cause excessive drowsiness. Antiepileptics and antidepressants are now also believed to carry similar risks. In the period covered by the source, motor vehicle crashes increased, and experts attributed part of that rise to the use of impairing prescription drugs. Workers in driving-intensive jobs are generally expected to notify their employers when prescribed such medications. If a worker must drive, the general guidance is that their healthcare provider should avoid prescribing opioids; if opioids are medically necessary, the employer is expected to assign duties that do not involve operating safety-sensitive equipment such as forklifts or cranes. The Royal Canadian Mounted Police has trained drug recognition and evaluation officers specifically to detect drug impairment through physical examinations and coordination tests, a capacity that Canadian provincial legislation has moved to formalize.

• 6. Penalties and Global Approaches

  ›

  The laws governing DUI vary significantly from country to country, particularly in the blood alcohol thresholds that trigger a criminal charge. Most nations use some combination of sobriety checkpoints, license suspensions, fines, and prison sentences as deterrents. Public awareness campaigns in many countries use advertising to discourage impaired driving and encourage the use of taxis or public transport after consuming alcohol or other drugs.

  In some jurisdictions, civil liability can reach beyond the driver. A bar or restaurant that serves a visibly impaired customer who then causes a crash may face its own legal exposure. Advocacy organizations such as Mothers Against Drunk Driving, known as MADD, run independent publicity campaigns against drunk and impaired driving separate from government efforts.

  In the United States, federal regulation through the Department of Transportation adds a layer beyond state DUI statutes. Commercial Driver's License holders face a one-year CDL suspension for a single DUI arrest and lifetime CDL revocation if they are subsequently arrested a second time for driving impaired. The USDOT also enforces a zero-tolerance cannabis policy for all regulated employees, applicable whether the worker is on-duty or off-duty, regardless of the laws in the state where they work.

  In Colorado, impaired drivers arrested with minor children in the vehicle may face an additional child endangerment charge. Separately, a practice called "wet reckless" allows defendants in some states to plead guilty to reckless driving in exchange for dropping the drunk driving charge. California does not allow a driver to be charged directly with wet reckless; it can only arise as a plea bargain outcome after a DUI charge has been filed. Looking ahead, the European Union in 2025 proposed an EU-wide two-year probationary period without alcohol as part of new rules for the European driving license, though member states retain the option to apply stricter standards.