Drunk Driving Terminology - DUI, DWI, BAC, and Related Terms

Commonly used terms in drunk and impaired driving cases include:


  • DWI - Driving While Impaired

  • DUI - Driving Under the

  • OMVI - Operating a Motor Vehicle while Impaired

  • OUI - Operating Under the Influence

  • OUID - Operating Under the Influence of Drugs

  • OUIL - Operating Under the Influence of Liquor

  • OWI - Operating While Impaired

  • "Per Se" Offense - A drunk driving offense which can result in conviction based upon proof of blood alcohol content (BAC), without any proof of impairment of ability to drive.

  • UBAL - Unlawful Blood Alcohol Level

Testing Devices (Breathalyzer Tests)

  • BAC Datamaster - A breath analysis device that produces an estimate of blood alcohol based upon infrared spectroscopy. These devices are designed to be low-maintenance, and relatively easy to use. However, they are not foolproof, and mistakes may occur in calibration, maintenance and storage, operation and use of the devices. A BAC device may also detect presence of chemicals other than alcohol, for example detecting acetone in the breath of diabetics.

  • Breathalyzer - A breath analysis device that produces an estimate of blood alcohol based upon the chemical analysis of a breath sample. These devices have largely been phased out due to new technologies that are less difficult to administer and less prone to error. However, due to their prior wide use, many people still refer to any breath testing device as a "breathalyzer".

  • Intoxylizer - A breath analysis device which produces an estimate of blood alcohol based upon infrared spectroscopy.

  • Intoximeter - Intoximeter devices are based upon fuel cell technology, infrared spectroscopy, or a combination thereof. Fuel cell technology involves the chemical analysis of a breath sample, to create a measurable electrical reaction which provides a measure of breath alcohol concentration. Early models of this device were susceptible to error from radio frequency interference.

  • PBT - Preliminary Breath Test - A PBT device is portable in nature, and is often carried by police in the field. PBT devices provide an estimate of blood alcohol concentration. However, due to the nature of the devices and the circumstances under which they are used, PBT results are not ordinarily admissible in court except under unusual circumstances.

Field Sobriety Tests

Field or Roadside Sobriety Tests are used to establish probable
cause for administration of a preliminary breath test, or for a drunk driving
arrest and administration of a formal breath or blood test.

  • The Standardized Field Sobriety Test (SFST) is a battery of three tests administered and evaluated in a standardized manner to obtain validated indicators of impairment and establish probable cause for arrest. The tests administered under this protocol are the horizontal gaze nystagmus test, the walk-and-turn test, and the one-leg stand.

  • Divided Attention Testing - Tests which require a suspect to listen to and follow instructions while performing simple physical movements. Such tests include the walk-and-turn test and one-leg stand test.

Commonly administered sobriety tests include:

  • Counting - The suspect is asked to count forwards or backwards, usually by ones or threes. Signs of impairment include (1) skipping letters, (2) loss of concentration, and (3) slurred speech. This is not a particularly accurate or reliable sobriety test.

  • Finger to Nose - The suspect stands, usually with the head tilted back and eyes closed, with arms stretched out to his sides. The suspect then attempts to touch the tip of his index finger to his nose, first with one arm and then the other. Signs of imparment include (1) beginning before instructions are completed, (2) swaying or staggering, (3) using arms to balance, (4) losing balance, and (5) inability to touch fingertip to nose. This test can be difficult to perform even when sober, without practice.

  • Reciting the Alphabet - The suspect is asked to recite the alphabet, sometimes backwards. Signs of impairment include (1) skipping letters, (2) loss of concentration, and (3) slurred speech. This test is not particularly accurate, and may not be appropriate for suspects for whom English is not the primary language.

  • Standing on One Leg - The suspect is instructed to stand on one leg, with the other foot suspended approximately six inches off the ground and count aloud by thousands ("One thousand-one", "one thousand-two", etc.) until instructed to put the foot down. The officer times the suspect for thirty seconds. The officer looks for indicators of impairment, including (1) swaying while balancing, (2) using arms to balance, (3) hopping to maintain balance, (4) not counting in order, and (5) putting the foot down.

  • Walking a Line - A suspect is asked to walk a straight line. This should occur on a flat, even surface, at a safe distance from traffic. The officer looks for signs of impairment including (1) beginning before instructions are completed, (2) swaying or staggering, (3) using arms to balance, and (4) stopping walking to regain balance.

  • Walk-and-Turn - A suspect is instructed to take nine steps along a straigt line, walking heel-to-toe. After taking the steps, the suspect must turn on one foot and return in the same manner in the opposite direction. The examiner looks for seven indicators of impairment: (1) if the suspect cannot keep balance while listening to the instructions, (2) begins before the instructions are finished, (3) stops while walking to regain balance, (4) does not touch heel-to-toe, (5) uses arms to balance, (6) loses balance while turning, or (7) takes an incorrect number of steps.

  • Horizontal Gaze Nystagmus - Horizontal gaze nystagmus is an involuntary jerking of the eyeball which occurs naturally as the eyes gaze to the side. This test theorizes that when a person is impaired by alcohol, nystagmus is exaggerated, and that alcohol-impaired person will have difficulty smoothly tracking a moving object. To administer this test, an officer asks the suspect to watch a slowly moving object, such as a pen or small flashlight. As the officer moves the object horizontally (back and forth), the officer watches the suspect's eyes as they follow the object, watching for signs that (1) the eye cannot smoothly follow a moving object, (2) distinct jerking when the eye is at maximum deviation, and (c) an angle of onset of jerking within 45 degrees of center. The presence of four or more signs between a suspect's two eyes is considered to suggest unlawful intoxication. The circumstances of a roadside administration, or a lack of training for the officer administering the test, can significantly affect test results.

Additional Terms:

  • Administrative Penalty - A sanction which may be imposed through an administrative agency, such as a state department of motor vehicles (DMV), even without criminal prosecution.

  • BAC - Blood Alcohol Content, usually expressed in a number reflecting the ratio of milligrams of alcohol in 100 milliliters of blood.

  • BAL - Blood Alcohol Level. The same as Blood Alcohol Content.

Copyright © 2003 Aaron Larson, All rights reserved. No portion of this article may be reproduced without the express written permission of the copyright holder. If you use a quotation, excerpt or paraphrase of this article, except as otherwise authorized in writing by the author of the article you must cite this article as a source for your work and include a link back to the original article from any online materials that incorporate or are derived from the content of this article.

This article was last reviewed or amended on May 26, 2016.