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

Drunk and impaired driving cases can be confusing due to the terminology used by police and the courts. What do commonly used terms and abbreviations mean?

Commonly used terms in drunk and impaired driving cases include:


  • DWI: Driving While Impaired

  • DUI: Driving Under the Influence

  • 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 that 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 that 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 that 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, absent unusual circumstances PBT results are not ordinarily admissible in court.

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): The SFSt is a protocol that involves the administration of three sobriety tests, the horizontal gaze nystagmus test, the walk-and-turn test, and the one-leg stand. The administration and evaluation of the tests is performed in a standardized manner, with the goal of obtaining a valid assessment of impairment and to establish probable cause for the arrest of an impaired driver.

  • Divided Attention Testing: Sobriety tests that require a suspect to both listen to and follow instructions while performing simple physical movements are classified as divided attention tests. Examples include the one-leg stand test and the walk-and-turn test.

Commonly administered sobriety tests include:

Counting Test

For the counting test, a suspect is asked to count forwards or backwards, usually by ones or threes.

Signs of impairment that may be observed by an officer include:

  • Skipping numbers,
  • Slurred speech, and
  • Loss of concentration.

The counting test is not a particulary reliable or accurate test of sobriety.

Finger to Nose Test

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 impairment 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

For this test the suspect is asked to recite the alphabet. The request may involve reciting the alphabet forwards or backwards.

The officer who administers the test watches for signs of impairment that include:

  • Skipping letters,
  • Loss of concentration, and
  • Slurred speech.

This test is not considered to be a particulary good measure of intoxication. This test also may not be inappropriate when English is not the suspect's primary language.

Standing on One Leg

For this test, the suspect is instructed to stand on one leg. The suspect is instructed to hold the other foot approximately six inches off the ground and to count aloud by thousands ("One thousand-one", "one thousand-two", etc.) until instructed to put the foot down. Once the test begins, the officer times the suspect for thirty seconds.

The officer looks for indicators of impairment including:

  • Does the suspect sway while balancing,
  • Does the suspect use his or her arms to balance,
  • Does the suspect hop to maintain balance,
  • Does the suspect count out of order, and
  • Does the suspect put the suspended foot down before the test is complete.

Walking a Line Test

For this test, the suspect is asked to walk a straight line. The test should be performed on a flat, even surface, and at a safe distance from traffic.

When observing a suspect walk a line, the officer looks for signs of impairment including:

  • Does the suspect start to walk before instructions are completed,
  • Does the suspect sway or stagger while walking,
  • Does the suspect use his or her arms to balance, and
  • Does the suspect stop walking before completing the test in order to regain balance.

Walk-and-Turn Test

In the walk-and-turn test, a suspect is instructed to walk heel-to-toe, and to take nine steps along a straight line. After the suspect completes the steps, the suspect must turn on one foot and walk back in the opposite direction, again heel-to-toe. The officer conducting the test looks for seven possible indications of impairment:

  1. Can the suspect keep balance while listening to the instructions,
  2. Does the suspect begin to walk before the instructions are finished,
  3. Does the suspect stop while walking in order to regain balance,
  4. Does the suspect consistently touch heel-to-toe,
  5. Does the supect need to use his or her arms to balance,
  6. Does the suspect lose balance while turning, or
  7. Does the suspect take an incorrect number of steps when completing the test.

Horizontal Gaze Nystagmus Test

Horizontal gaze nystagmus is a term for involuntary bouncing or jerking movements of the eyeball that naturally occur as a person looks or gazes the side. The horizontal gaze nystagmus test is based upon the theory that when a person is impaired by alcohol, nystagmus becomes exaggerated and as a result impaired persons will have difficulty smoothly tracking a moving object with their eyes.

When administering this test, the officer will ask the suspect to watch a slowly moving object, such as a small flashlight or the end of a pen. The officer moves the object back and forth horizontally, and watches the suspects eyes. Signs that may indicate impairment include:

  • The suspects eyes cannot smoothly follow a moving object;
  • The suspect's eyes show distinct jerking movements when the eye is at maximum deviation;
  • Jerking movements of the eye begin within forty-five degrees of center.

If after testing both eyes an officer detects four or more signs of impairment, the test result incidates that the driver is intoxicated.

The horizontal gaze nystagmus test may be affected by the quality of the officer's training in administering the test, and also based upon the circumstances under which the test is administered at roadside.

Additional Terms:

  • Administrative Penalty: A sanction tht may be imposed by an administrative agency even if no criminal prosecution occurs. For example, state department of motor vehicles (DMV) may impose driver's license sanctions against a driver who is charged with impaired driving or refuses a lawful request to submit to roadside sobriety testing.

  • 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 8, 2018.