If you have been stopped by the police for traffic violation and the officer notices any sign that you may have been drinking, he will likely initiate a DUI investigation.  Common signs of alcohol consumption which police officers will look for include an odor of alcohol, blood shot or watery eyes, slurred speech, an admission of drinking, etc.  Once an officer decides to investigate you for DUI, he will request that you step out of your car and participate in a series of tests called "Field Sobriety Tests" or "Field Tests."

The Theory Behind Field Sobriety Tests:

Most field sobriety tests require a person to perform a mental and physical task at the same time.  This may include walking in a heel to toe manner while counting a specific number of steps or standing on one leg while counting to thirty.  Proponents of the field sobriety tests analogize these simultaneous physical and mental tasks to driving a vehicle where a person must maintain a safe speed, keep the vehicle within their own lane and look out for other vehicles on the roadway.  

While administering the field sobriety tests, officers will look for specific mistakes or "clues of impairment."  When officers observe the clues, he will likely conclude that you are impaired by alcohol to operate a motor vehicle.  Additionally, the National Highway Traffic Safety Administration states that the field tests can also be utilized to predict whether a person's blood alcohol concentration is above the legal limit of .08.

What Field Tests Are Often Used in DUI Investigation:

Although there are a number of field sobriety tests that officers may use when conducting a DUI investigation, only three have been subject to any studies to determine whether they are reliable.  These include:

1. Horizontal Gaze Nystagmus

The Horizontal Nystagmus Test (HGN) is a standardized field sobriety test (FST) that police often administer in order to gauge whether a DUI suspect is under the influence of alcohol.

The officer instructs the suspect to follow a stimulus  such as the tip of a pen or a light with his eyes to the left and to the right. The officer notes the angle at which the pupil starts to exhibit "nystagmus" (an involuntary jerking of the eye). An early onset of nystagmus (at or before a 45-degree angle) is a clue associated with a high blood alcohol concentration.

According to the National Highway Transportation Safety Administration, studies have revealed the HGN Test to be 77% reliable in determining whether a driver has a blood alcohol concentration above the legal limit.

2. Walk and Turn Field Test:

In the walk-and-turn test, you are instructed to take nine steps in a heel-to-toe fashion in a straight line.  You are required to keep your arms at your sides and cannot miss touching heel to toe by more than a half inch. After the ninth step, you then must pivot without lifting your feet and return in the opposite direction in a heel-to-toe fashion. 

While you are completing the walk-and-turn test, the police officer is looking for the following mistakes: 

(1) whether you are unable to maintain your balance while listening to the officer's instructions;

(2) whether you begin walking before the officer has completed the instructions;

(3) whether you stop while walking in order to regain your balance;

(4) whether you actually touch your feet heel-to-toe;

(5) whether you use your arms to maintain your balance;

(6) whether you lose your balance while turning;

(7) whether you take an incorrect number of steps. 

Usually if you make two or more mistakes on the walk and turn test, you are considered to have failed.

3. One Leg Stand Test:

The one-leg stand test is another standardized field sobriety test (SFST) that police often administer as a means to determine whether a DUI suspect is under the influence of alcohol or drugs.

In the one-leg stand test, officers instruct the suspect to stand with one foot approximately six inches off the ground and count aloud by thousands (one thousand-one, one thousand-two, etc.) until told to put the foot down (which should happen after 30 seconds). The suspect is further instructed to keep his eyes on the elevated foot and keep his arms by his sides while performing the test.

Errors the officer is looking for on this test include:

 (1) A sway while balancing on one leg

 (2) Using  or raising arms to balance

 (3) Hoping

 (4) Putting a  foot down,

Again, if you make two or more mistakes on the walk and turn test, you are considered to have failed.

Should You Participate in Field Sobriety Tests:

Many people confuse the field tests in a DUI investigation with the blood or breath tests that officers require them to take.  In contrast to a blood, breath or urine test which officers will request following a DUI arrest, participation in field sobriety tests is completely voluntary.  Specifically, people who refuse to take a blood, breath or urine test after being arrested for DUI in Arizona risk a one year revocation of their drivers license.  This is referred to as the "Implied Consent Statute."

There is no mandatory penalty or loss of license for refusing to do the field tests.  Although a prosecutor may refer to your refusal to take the tests as evidence that you were impaired or knew you were impaired, there is no law which requires a person to take the eye test, walk and turn test, one leg stand test or any other field sobriety test.  Moreover, most people are at risk of failing the divided attention tests because of nervousness, poor coordination and outside influences such as weather, traffic or onlookers.  

If you find yourself being investigated for DUI and are asked to participate in field testing, you should politely decline and request to consult with an attorney as soon as possible.    

If you, a family member or loved one has been charged with DUI or any other criminal offense in Arizona you are well advised to immediately contact an experienced DUI or criminal defense lawyer who regularly represents people charged with these types of offenses.  Attorney Raymond Kimble has represented people charged with DUI and other crimes in  Tempe, Mesa, Chandler Phoenix, Scottsdale and other cities throughout Maricopa and Pinal Counties during the last twenty years and has achieved tremendous results for his clients.