DUI & Criminal Defense

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Arizona Driving While Impaired (Updated 2019)


Here is what it means to be “impaired” under an Arizona DUI law

Impairment​ as a Matter of Law

Arizona law has created two ways to violate the first offense DUI laws: 

  • Driving while impaired to the slightest degree by alcohol or a drug; or
  • having an alcohol concentration above a statutory limit within 2 hours of driving.

So, how do you define “impaired to the slightest degree”?  Let’s find out.

In the beginning…

Arizona has had some version of a DUI Law since late 1920. In every version of our DUI statutes, the Arizona legislature has never specifically defined what they meant by impaired driving.

The legislative history of Arizona’s DUI law (A.R.S. 28-1381) does not tell us the reason why they left such an important term up for interpretation. While there were probably several reasons, one seems fairly obvious, once you understand what impairment really means in the context of alcohol consumption. That is, you cannot determine if a person is impaired at performing a task (like walking, standing on one leg, or dancing) unless you know how they normally perform that task – without consuming alcohol. More on this below.

Under the Influence v. Impaired

The law makes an important, but often overlooked, distinction between being under the influence of alcohol and being impaired by alcohol. Let’s look at the jury instruction  in a DUI case where a person is alleged to have been driving and impaired by alcohol: 

Arizona DUI First Offense Laws

There are three essential elements of a first offense Arizona DUI:

  • Driving or Actual Factual Control
  • Under the Influence of an Intoxicating Liquor or Drug... [AND]
  • Impaired to the Slightest Degree

Notice that the proof of a person was under the influence of alcohol is not sufficient to make them guilty of the DUI.  To illustrate, you can consume alcohol resulting in a flushed face or a feeling relaxed.  That is just being under the influence of an intoxicating beverage.  However, impairment goes beyond those effects.

Your Specific Baseline

The effects of alcohol on the human body are studied by Toxicologists.  In the field of toxicology, impairment is defined as a measurable difference between the way a person normally performs a task, and how they perform the same task less effectively, because of the consumption of alcohol.  

To determine if any form of impairment is present you need to know what a person’s baseline abilities are for that task.  A police officer who meets you for the first time – during a traffic stop – has no way to know your baseline motor skill abilities for any given task.

Stages of Alcohol's Effects

Dr. Kurt Dubowski was considwred one of the foremost expert’s regarding the effectsof alcohol on the humna body. In 1953, he conceived and subsequently published a chart illustrating the stages of Alcohol Infuence that is still used today in impaired driving cases.  His BAC interpretation table was updated in 2012.

grams/100 mL



Influence/effects usually not apparent or obvious. Behavior nearly normal by ordinary observation. 



  • Mild euphoria
  • Sociability
  • Talkativeness
  • Increased self-confidence
  • Decreased inhibitions
  • Diminished attention, judgment and control
  • Some sensory-motor impairment
  • Slowed information processing
  • Loss of efficiency in critical performance tests.



  • Emotional instability
  • Loss of critical judgment
  • Impairment of perception memory and comprehension
  • Decreased sensitory response
  • Increased reaction time
  • Reduced visual acuity & peripheral vision; and slow glare recovery
  • Sensory-motor incoordination
  • Impaired balance
  • Slurred speech
  • Vomiting
  • Drowsiness.


  • Disorientation
  • Mental confusion
  • Vertigo
  • Dysphoria
  • Exaggerated emotional states (fear, rage, grief, etc)
  • Disturbances of vision (diplopia, etc.) and of perception of color, form, motion, dimensions
  • Increased pain threshold
  • Increased muscular incoordination
  • Staggering gait
  • Ataxia
  • Apathy
  • Lethargy



  • General inertia
  • Approaching loss of motor functions
  • Markedly decreased response to stimuli
  • Marked muscular incoordination
  • Inability to stand or walk
  • Vomiting
  • Incontinence of urine and feces
  • Impaired consciousness
  • Sleep or Stupor



  • Complete unconsciousness
  • Coma
  • Anesthesia Depressed or abolished reflexes
  • Subnormal temperature
  • Impairment of circulation and respiration
  • Possible death



Death from respiratory arrest.

Here is a downloadable copy of the Dubowski Chart

The Progression of Alcohol's Effects

Progression of Alcohol Impairment

The specific effects – of a specfic alcohol concentration – will vary to some degree from person to person. However, the order of things effected by alcohol in the human body always remains the same.  It’s a rigid progression.  If the observed symptom do not fit this progress then alcohol is likely not the cause of the impairment.

To determine if any form of impairment is present you need to know what a person’s baseline abilities are for that task.  A police officer who meets you for the first time – during a traffic stop – has no way to know your baseline motor skill abilities for any given task. 

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