Driving under the influence (driving while intoxicated, drunk driving, operating under the influence, drinking and driving, drink-driving, impaired driving) is the act of operating any motorized machinery after/during consuming alcohol or other drugs. DUI or DWI are synonymous terms that represent the criminal offense of operating (or in some jurisdictions merely being in physical control of) a motor vehicle while being under the influence of alcohol or drugs or a combination of both. It is a criminal offense in most countries.
All American states have also enacted per se laws that prohibit operating (or in some jurisdictions merely being in physical control of) a motor vehicle while having a specific blood alcohol content (BAC) level. One can be prosecuted under the per se laws whether or not they are actually "impaired" or "under the influence" of alcohol.
In most countries, anyone who is convicted of injuring or killing someone while under the influence of alcohol or drugs can be heavily fined, as in France, in addition to being given a lengthy prison sentence. Many states in the U.S. have adopted truth in sentencing laws that enforce strict guidelines on sentencing. For example, if a defendant is sentenced to ten years, he or she will be in prison for that entire time. This is different from past practice where prison time was reduced or suspended after sentencing had been issued.
The specific criminal offense may be called, depending on the jurisdiction, driving under intense influence (DUII), driving while intoxicated (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, driving under the influence per se or drunk in charge [of a vehicle]. Other less common acronyms include ("OVI"), "operating a vehicle (while) impaired," and ("DWAI"), "Driving While Ability Impaired." Many such laws apply also to boating, piloting aircraft, riding a horse or conducting a horse-drawn vehicle, or cycling.
With the advent of a scientific test for blood alcohol content (BAC), enforcement regimes moved to pinning culpability for the offense to strict liability based on driving while having more than a prescribed amount of blood alcohol, although this does not preclude the simultaneous existence of the older subjective tests. 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 milliliters 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 at least 2004, it has been illegal in all US states and the District of Columbia to drive with a BAC that is 0.08% or higher. Canada adopted similar laws in the 1990s.
The validity of the testing equipment/methods and mathematical relationships for the measurement of breath and blood alcohol have been criticized. (Taylor 2007)
Driving while consuming alcohol may be illegal within a jurisdiction. In some it is 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. In some it may be illegal to be asleep in the driver's seat of a vehicle without any intention to drive.
The German model serves to reduce the number of accidents by identifying unfit drivers and removing them from traffic until their fitness to drive has been established again. The Medical Psychological Assessment (MPA) works for a prognosis of the fitness for drive in future, has an interdisciplinary basic approach and offers the chance of individual rehabilitation to the offender.
Historically, guilt was established by observed driving symptoms, such as weaving; administering field sobriety tests, such as a walking a straight line heel-to-toe or standing on one leg for 30 seconds; and the arresting officer's subjective opinion of impairment. The officer must correctly perform the Field Sobriety Tests (FST's) that are approved by the National Highway Transportation Safety Administration (NHTSA). There are only three (3) FST's federally approved by NHTSA. The US Department of Transportation explains the Field Sobriety Test as, "a battery of three tests administered and evaluated in a standardized manner to obtain validated indicators of impairment and establish probable cause for arrest." 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 supplanted the earlier purely judgmental ones. Limits for chemical tests are specific for blood alcohol concentration or concentration of alcohol in breath.