other: Under the influence

Driving under the influence of alcohol (driving while intoxicated, drunk driving, drinking and driving, drink-driving) or other drugs, is the act of operating a motor vehicle (and even a bicycle, boat or horse in some jurisdictions) after having consumed alcohol, to the degree that mental and motor skills are impaired. It is a crime or offense in most countries around the world.

Overview

In most international jurisdictions, anyone who is convicted of injuring or killing someone while under the influence of alcohol or drugs can be heavily fined, as in France,1 in addition to being given a lengthy prison sentence.

The specific criminal offense may be called, depending on the jurisdiction, driving while intoxicated (DWI), operating while intoxicated (OWI), operating a motor vehicle while intoxicated (OMVI), driving under the influence 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 a vehicle. Such laws may also apply to boating (as in Canada2), piloting aircraft, and even bicycling in some states such as California.

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. 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. Limits for chemical tests are specific for blood alcohol concentration or concentration of alcohol in breath.

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 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.