DUI Field Sobriety Evaluations

DUI investigations usually begin when you are initially detained by police. Most of the time, that is after being stopped at a roadblock, allegedly committing a traffic violation, or being involved in an accident. If the officer thinks you might be an impaired driver, he or she will typically ask you to perform field sobriety evaluations. Officers often ask people to perform these evaluations if they smell an alcohol beverage on the driver breath, they notice red or bloodshot eyes, or the driver admits to drinking. While the officer might not tell you they are voluntary, they ARE voluntary. There is no legal consequences for refusing to perform these evaluations. Many attorneys advise people to always refuse field sobriety evaluations if asked to perform them. While that is often good advice because it limits the amount of evidence against you in a DUI case, you are almost guaranteed to be arrested if you are asked to perform field sobriety evaluations and refuse to do so. Your performance on the field sobriety evaluations can depend on a variety of factors, including but not limited to:

  1. Your physical state, which can include fatigue or nervousness.
  2. Your coordination and balance.
  3. How much you have had to drink.
  4. Any medication or drugs you have consumed.
  5. The weather and roadside conditions, including the grade of the road or parking lot.
  6. What type of shoes you wearing.
  7. The investigating officer instructions and demeanor.

Where Do Field Sobriety Evaluations Come From and What Are They?

In 1977, the National Highway Traffic Safety Administration (“NHTSA”), which is an agency of the federal government, commissioned a study to by the Southern California Research Institute to evaluate and standardize different roadside tests used by police to determine if drivers are impaired. They reached the conclusion that a standard battery of three evaluations should be performed to evaluate drivers that police suspect might be impaired.

NHTSA periodically publishes a teaching manual that is used across the country by law enforcement agencies to train police officers on how to perform these evaluations, as well as other clues to look for in making a DUI arrest. It important to note that a good portion of funding that individual states receive for highway construction and grants for patrolling those highways come through NHTSA. And there are strings attached. A major reason why every state has a per se limit of 0.08 for DUI cases is that NHTSA will reduce funding for any state that raises that limit any higher. So these standardized evaluations are supposed to be done the same way every time, with no flexibility for people of varying age, weight, coordination, disabilities, or varying roadside conditions. Officers might also use other evaluations, such as the finger to nose test or the alphabet test. None of these have been studied to correlate to alcohol use or impairment. Here are the three evaluations officers are taught to perform:

Horizontal Gaze Nystagmus (HGN)

The purpose of the HGN evaluation is to use a stimulus, which is typically either the officer finger or a pen, to see if the suspect has nystagmus. This is done by moving the stimulus back and forth horizontally, slightly above eye level, about 12-15 inches from the face. Nystagmus is the involuntary jerking of the eye, which can have a variety of causes. Alcohol consumption is one of those possible causes, but there are many others, such as a congenital disease or a head injury.

Officers are trained to ask the suspect if they have any medical conditions and if they think you might have a condition, such as a concussion, that causes nystagmus, then they are not supposed to perform the evaluation. A second check for candidates is to make sure the suspect does not have resting nystagmus and that his/her eyes track equally. Based on the questions and these two preliminary checks, the officer either performs the evaluation with limited information, or not at all. There is no alternative.

There are 6 total clues the officer looks for, with 3 from each eye:

  1. Lack of smooth pursuit of the eyes;
  2. Distinct and sustained nystagmus at maximum deviation;
  3. Onset of nystagmus prior 45 degrees.

These clues are also determined by looking for involuntary jerking of the eye when the suspect follows the stimulus with his or her eyes without moving his or her head. The studies as it relates to HGN and the other evaluations do not correlate to one general impairment, but rather a percentage likelihood that the person BAC is 0.08 or greater. If the officer observes 4 or more clues, the NHSTA guidelines say it 88% reliable that the suspect BAC is .08 or greater.

Walk & Turn

This evaluation is performed after the officer instructs the suspect to stand with their right foot in front of their left, heel to toe, and to stay in that position until told to start. The suspect is instructed to walk nine heel to toe steps on an imaginary or actual line, turn around with a series of small steps, then walk nine heel to toe steps back. The instructions also include keeping one’s arms at their side, and to not stop until the evaluation is completed. The officer is supposed to demonstrate how it is done, but only does 3 steps instead of 9. Per NHSTA guidelines, here are the 8 clues the officer looks for:

  1. Starting the Evaluation Too Soon, i.e. walking the line before being told to do so
  2. Failing to Remain in the Instructional Stance
  3. Stepping Off Line While Walking
  4. Missing Heel to Toe While Walking
  5. Raising Arms for Balance
  6. Incorrect Number of Steps
  7. Improper Turn
  8. Stops Walking

According to NHTSTA, if the person shows 2 or more of these clues, it 79% reliable that the person BAC is 0.08 or higher. There is no weight given to certain clues, and no sliding scale. It simply ANY two clues.

One Leg Stand

This evaluation is performed after the officer instructs the person to raise either foot approximately 6 inches off the ground, keeping their arms by their side, and counting out loud until told to stop. Here are the 4 clues the officer is trained to look for:

  1. Raises arms for balance
  2. Puts foot down
  3. Sways
  4. Hops

According to NHTSA guidelines, 2 or more clues indicate it 83% reliable that the suspect BAC is 0.08 or greater.

It also important to know that these field sobriety evaluations are NOT Pass/Fail. Officers look for a certain minimum number of clues to determine whether to arrest you for DUI. So you might show no clues on one of the three evaluations, but they will often still arrest you if you performed poorly on the other two.

I don't think everyone should refuse to do field sobriety evaluations 100% of the time. There can be situations for the coordinated person who hasn't had that much drink that exhibits minimal clues on these evaluations and is not arrested for DUI. These situations are not the norm, but do occasionally occur. Clues exhibited on these evaluations are often crucial evidence that prosecutors rely upon when trying to convict people of DUI.

These evaluations can be challenged in court both for their reliability and how they are conducted by police officers. It helps to have an attorney experienced in DUI cases representing you in court whether you performed these or not.


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