DUI : DRIVING UNDER THE INFLUENCE

"DUI" offense consists of driving under the combined influence of alcohol and other drugs. The drugs causing or contributing to the impairment need not be illegal, but can consist of lawfully prescribed or over-the-counter medication. Anti-drunk-driving advertising campaigns have aimed to raise awareness of the legal situation and the dangers of driving while intoxicated. Drunk-driving is responsible for a large number of deaths, injuries, damage and accidents every year.

The specific criminal offense may be called, depending on the jurisdiction, driving while intoxicated (DWI), driving while impaired (also DWI), operating while intoxicated (OWI), operating a motor vehicle while intoxicated (OMVI), driving under the influence [of alcohol or other drugs] (DUI), driving under the combined influence of alcohol and/or other drugs or drunk in charge [of a vehicle]. Such laws may also apply to boating, or piloting aircraft.

Historically, guilt was established by subjective tests of the driver's impairment, such as difficulty reciting the alphabet or walking a straight line, together with the arresting officer's subjective opinion. Starting with the introduction in Norway in 1936 of the world’s first per se law which made it an offense to drive with more than a specified amount of alcohol in the body, objective chemical tests have gradually supplemented the earlier purely judgmental ones.

Today's statutes commonly provide for two separate and distinct criminal offenses. The first is the traditional "drunk driving" offense, consisting of driving under the influence of alcohol and/or drugs. Evidence to support this crime generally comes from the officer's observations (erratic driving, slurred speech, unsteady gait, etc.), performance on field sobriety tests, and a legal (and generally rebuttable) presumption of intoxication from a blood alcohol test result over the legal limit. The second offense is the more recent so-called "per se" offense: rather than focusing on impairment the crime consists entirely of having a given blood alcohol content (BAC) at the time of driving, regardless of the individual's tolerance to alcohol. Both offenses may be charged, and the defendant may be convicted of both; if a blood alcohol test result was not obtained, only the traditional "DUI" offense will be charged.

BAC is most conveniently measured as a simple percent of alcohol in the blood by weight. It does not depend on any units of measurement. In Europe it is usually expressed as milligrams of alcohol per 100 millilitres of blood. However, 100 milliliters of blood weighs essentially the same as 100 milliliters of water, which weighs precisely 100 grams. Thus, for all practical purposes, this is the same as the simple dimensionless BAC measured as a percent. Since 2002 it has been illegal in all 50 US states to drive with a BAC that is 0.08% or higher.

Driving while consuming alcohol is generally illegal, though driving after drinking remains legal. In some jurisdictions it is also illegal for an open container of an alcoholic beverage to be in the passenger compartment of a motor vehicle or in some specific area of that compartment.