• The best way to avoid a DUI investigation and charge is to never drink and drive.   However, if it is too late for this advice and you have been pulled over by a police officer, here is the process the officer will go through to determine whether to arrest you for driving under the influence of alcohol or drugs. 

STAGE ONE:  Observing The Vehicle In Motion

  • People operating a vehicle under the influence will generally exhibit symptoms of impairment.  The officer will look for slowed reactions, a willingness to take risks, poor coordination and impaired vision.  The vehicle might be going extremely fast or extremely slow.  There may be a violation of a posted control sign, a failure to use a turn signal, inappropriate use of high beams or any number or other clues that alert the officer to a probability that the driver is influenced by intoxicants.

  • All an officer needs to justifying pulling a vehicle over is a reasonable belief that the driver was operating in an unreasonable manner, or a reasonable suspicion that a traffic law has been violated.  A good faith belief on the officer's part that the driver may be physically unfit to drive may suffice. 

  • Officers look for 20 specific visual cues that indicate that the driver may be legally intoxicated.  If observed independently of any other behavior, each clue has a corresponding probability of impairment established by the National Highway Transportation Safety Administration (NHTSA).  They are as follows:



Headlights off


Accelerating or decelerating rapidly


Turning abruptly or illegally


Stopping inappropriately (other than in the lane of travel)


A slow response to traffic signals


Driving into or crossing traffic


Erratic application of the brakes


Driving with tires on center or lane marker




Following too closely


Stopping without cause in the lane of traffic


Driving slower than 10 miles per hour




Driving on other than the designated highway




Almost striking object or vehicle


Appearing to be drunk:  (eye fixation; tightly gripping the steering wheel; gesturing erratically or obscenely; face close to the windshield; drinking in the vehicle; driver's head protruding from vehicle)



Straddling center or lane marker


Turning with wide radius


  • The probabilities listed above correspond to the officer seeing only one cue.   When the officer observes a combination of several cues, the probability rises.

  • When an officer initiates a traffic stop, there is opportunity for the observation of several more cues of impairment.  The stopping sequence that the suspect uses will often be used at trial to prove that the driver was under the influence.  Some of the observations typically include:

  1. Attempt to flee;

  2. A slowed response in pulling over;

  3. No response to the officers lights, siren, and commands;

  4. Abrupt swerve;

  5. Sudden stop;

  6. Stopping in an inappropriate place; and

  7. Hitting the curb or other object when pulling over.

  • At trial, prosecutors and officers almost always use the theory of "divided attention" to explain the process of impairment.  The ability to execute multiple tasks simultaneously, to divide attention, is greatly limited by alcohol or drugs in the system.  Once the police initiate the stop, there is an increased opportunity for them to look for cues of divided attention and impairment.  The intervention of the police officer(s), with flashing lights, sirens and megaphones requires complex motor and emotional processing on the part of the suspect.  Many drivers who are under the influence have trouble handling this situation.

  • Once the stop has been completed, the officer moves into the next stage of the DUI investigation.

STAGE TWO:  Personal Contact

  • Once the stop has been completed, the officer moves into the next stage of the DUI investigation - Personal Contact.   In this stage, the officer approaches, observes and interviews the driver while the driver remains in the vehicle.  The officer usually will ask the driver general questions to affirm or dispel the suspicion of DUI.  During these questions the officer will look for the following evidence of impairment: 
  1. What law enforcement commonly refers to as "The Odor Of Alcoholic Beverage About His/Her Person"  (This phrase is used repeatedly at most DUI trials);

  2. A flushed face;

  3. Bloodshot eyes; and

  4. Slurred or otherwise impeded speech.

NOTE:  If a police officer observes bad driving plus one or more of the above circumstances changes you are going to be arrested for DUI no matter what else happens.  The officer want to give you a breath test.  In Arizona, police can legally demand a breath/blood sample only if you are under arrest for DUI.  If a breath test is offered, take it.  If you refuse, the police will get a search warrant and take you blood by force if necessary.

  • The officer pays particular attention to how the driver produces the driver's license and registration.  The officer will note if the driver has trouble retrieving these documents from pocket or glove compartment.

  • During this time, the officer will also look around the vehicle for any evidence in plain view, such as beverage containers, drugs or drug paraphernalia. 

  • The officer may also administer some preliminary seated sobriety tests to help determine the driver's impairment.  These may be simple verbal exercises.  Once this is complete, the officer will decide whether to request that the driver get out of the vehicle.  Ordering the driver out of the vehicle does not necessarily commit the officer to arresting the driver, but it more times that not often ends up that way.

  • The officer will observe how the driver exits the vehicle.  Does the driver stumble, trip, use the door for support, fall or grab the officer for support.  Once the driver is out of the vehicle, the officer moves into stage three of the DUI investigation.

 STAGE THREE:  Pre-Arrest Screening

  • Once the driver is out of the vehicle, the officer moves into stage three of the DUI investigation, the pre-arrest screening phase.  

  • The officer's first task is to administer field sobriety tests.   These tests, many of which have been "standardized" by NHTSA, provide a judge or jury with objective descriptions of the clinical symptoms of impairment, and serve to reinforce the officers physical observations of the suspect during stage two of the investigation.

  • Officers know that a skilled defense attorney will scrutinize every detail of the tests.  On cross examination the defense attorney will try to discredit the test by asserting that: 

  1. The driver didn't understand the test adequately to perform it;

  2. The officer didn't first demonstrate the test;

  3. The lighting was insufficient;

  4. The road was hilly, rocky or otherwise unsmooth;

  5. Poor weather conditions;

  6. That driver had a physical defect which could affect the performance of the test.

  7. That the officer did not precisely follow the field sobriety test instructions

  • The officer will try to do everything possible to minimize the effects of such defense arguments. 

  • The "standardized" field sobriety tests that NHTSA recommends are as follows:

  • Horizontal Gaze Nystagmus

  • Walk and Turn

  • One Leg Stand

  • NEVER!, NEVER!, NEVER!, take field sobriety tests under any circumstances.  There is no requirement or penalty under the law for you to take field sobriety tests.  Note:  The breath test is not a field sobriety test.  

  • Other, non-NHTSA standardized field sobriety tests include:

  • Coin Toss Test

  • Finger To Nose Test

  • Balancing Tests 

  • Following the field sobriety tests, the officer may ask to give you a preliminary breath test (PBT), which the police use to confirm the chemical basis for the driver's impairment.  A preliminary breath test is for investigatory purposes only and is not admissible in court as evidence.  NEVER TAKE A PRELIMINARY BREATH TEST UNDER ANY CIRCUMSTANCES -- JUST POLITELY REFUSE THE OFFICER'S REQUEST.

  • If the officer is confronted with evidence of drug impairment, it will be necessary for an officer to seek assistance from an officer with special drug detection training, who will administer a standardized Drug Recognition Examination (DRE) of the suspect.

  • The arrest occurs at the conclusion of the pre-arrest screening process.   If the officer decides to arrest the suspect, he must have probable cause that the driver is under the influence of alcohol or drugs.

  • Once you are under arrest for DUI. the police will then invoke the "implied consent" statute and obtain a chemical test from you with a view towards establishing your Blood Alcohol Concentration (BAC). Never refuse a breath test or blood test.  The refusal will have serious consequences on your driver license and usually will result in the police getting a search warrant and taking you blood by force if necessary.

  • When you are on the road and under investigation for DUI by a cop, you are on their turf.  They have the power.  However, when you go into court with a DUI defense attorney, and your attorney cross-examines the cop, the cop is out of his/her element.   If the cop has made mistakes, a good DUI defense lawyer will make sure that the jury knows about them.

Copyright �  2006 Darby Law Office

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