Legal Definitions - D.U.I.

D.U.I. stands for Driving Under the Influence.

D.U.I. is a criminal offense that occurs when a person operates a motor vehicle while their ability to drive safely is impaired by alcohol, drugs (including prescription medications, over-the-counter drugs, or illegal substances), or a combination of these. This impairment can be established either by a blood alcohol concentration (BAC) at or above the legal limit (which is typically 0.08% in most U.S. states for drivers 21 and older) or by observable signs that the driver's mental and physical faculties are diminished to an extent that they cannot operate a vehicle as a reasonably prudent person would.

Here are some examples to illustrate D.U.I. in different contexts:

• Example 1: Alcohol Impairment Exceeding Legal Limit

  A person attends a social gathering and consumes several alcoholic beverages over a few hours. Believing they are "fine to drive," they get behind the wheel. A police officer later pulls them over for a broken taillight. During the stop, the officer notices a faint odor of alcohol and asks the driver to perform field sobriety tests, which they fail. A subsequent breathalyzer test reveals their BAC is 0.12%, significantly above the legal limit of 0.08%.

  This illustrates D.U.I. because the driver's blood alcohol concentration exceeded the legal threshold, establishing impairment by law, regardless of whether they personally felt intoxicated.

• Example 2: Drug Impairment from Prescription Medication

  An individual is prescribed a strong painkiller after a minor surgery. The medication's label clearly warns against operating heavy machinery or driving while taking it due to potential drowsiness and impaired judgment. Despite this, the person decides to drive to a pharmacy to pick up another prescription. While driving, they become disoriented and swerve into another lane, nearly causing a collision. A police officer witnesses this and pulls them over, observing slurred speech and slow reactions, even though no alcohol was consumed.

  This demonstrates D.U.I. because the driver's ability to operate the vehicle safely was impaired by a drug, even though it was legally prescribed. The impairment, not the legality of the substance itself, is the basis for the charge.

• Example 3: Combination Impairment with Observable Signs

  A driver takes an over-the-counter cold medicine that causes drowsiness and then has a single beer with dinner. Although their BAC is below the legal limit, the combination of the medication and the alcohol makes them feel unusually tired and unfocused. While driving home, they repeatedly drift out of their lane, miss a stop sign, and nearly hit a parked car. An officer stops them and observes significant impairment through their erratic driving, slow responses, and difficulty following instructions during field sobriety tests.

  This example shows D.U.I. based on the combined effect of substances. Even if neither the alcohol nor the medication alone would have caused impairment at a level to trigger a D.U.I., their synergistic effect diminished the driver's faculties, leading to observable impairment and a D.U.I. charge.