DUI Field Sobriety Tests

Field sobriety tests are conducted when a police officer suspects that a driver is impaired. Officers are trained to conduct the Standardized Field Sobriety Test, a set of three tests designed to determine a driver’s blood alcohol content (BAC). When administered correctly, officers typically can identify impaired drivers about 90 percent of the time.

Standardized Field Sobriety Tests

The National Highway Traffic Safety Administration has provided the following information regarding each of the three standardized sobriety tests:

Horizontal Gaze Nystagmus Test

Normal eyes experience involuntary movement known as "nystagmus" when they are rotated at large angles. However, drivers who are impaired will experience this eye movement at much smaller angles, accompanied by jerking when following an object. Officers use a small item, such as a flashlight or a pen, and slowly move that object in front of a driver’s eyes. An impaired driver will demonstrate one or more of these issues:

  • The inability to follow the object smoothly
  • Distinct jerking motions with sustained movement
  • Jerking when the eye has rotated less than 45 degrees

Drivers can also fail this test due to seizure medications, inhalants and some depressants, but it is still an accurate indicator of subjects with a BAC of .08 or higher approximately 88 percent of the time.

Walk-and-Turn Test

The most well-known of field sobriety tests, the walk-and-turn requires subjects to take nine forward steps in a straight line, touching heel to toe with each step. Then, the driver must turn around on one foot and repeat the nine steps in the opposite direction. There are many possible indicators of impairment in this test:

  • The inability to keep balance during the instructions
  • Beginning the test before the instructions are complete
  • Stopping to regain balance
  • Not touching heel to toe on every step
  • Using arms to keep balance
  • Walking off the straight line
  • Taking more or fewer than nine steps in either direction
  • Incorrectly turning

A 1998 validation study showed that 79 percent of drivers who meet two or more of these indicators had a BAC of .08 or higher.

One-Leg Stand Test

Subjects are told to stand on one foot with the other approximately 6 inches off the ground and to begin counting up from 1,000 out loud. They are to continue counting until they are told to put their foot down, usually counting for about 30 seconds. The testing officer looks for four possible impairment indicators:

  • Difficulty balancing, leading to swaying
  • Using the arms for balance
  • Hopping on one foot for balance
  • Putting the foot down too early

Individuals with a BAC of .10 or higher typically exhibit at least two of these indicators 83 percent of the time, according to research.

Each of these standardized tests was created to assess drivers’ coordination, steadiness and reaction time, which could be indicators of possible impairment. However, there could be other factors that lead to a failure of one or more of these tests, including things like age, an eye disease or condition or deafness, etc.

Non-standardized Field Sobriety Tests

Some states have held that evidence obtained from field sobriety tests is inadmissible in court and can only be used to validate an arrest. As a result, drivers who are suspected of being impaired are sometimes subjected to non-standardized tests. These could include:

  • Standing with their feet together while moving their head backward
  • Counting the number of fingers shown by the officer
  • Counting backward from a prescribed number
  • Reciting the alphabet both forwards and backward
  • Leaning backward with their arms to the side and looking up at the sky
  • Placing their fingers on their nose with their eyes closed

Although these tests are not the standard, they can be equally incriminating, especially if they are recorded by a video camera in the officer’s car. This type of footage is typically allowed as evidence in court.

What to Do After Failing a Field Sobriety Test

There is still some question about the validity and admissibility of field sobriety tests and there are reasons other than alcohol or drug impairment that could contribute to failing one. Therefore, people who have been taken into custody as a result of their performance on a field sobriety test may find it helpful to consult with a DUI attorney to find out the best course of action.

The information on this page is meant to provide a general overview of the law. The laws in your state and/or city may deviate significantly from those described here. If you have specific questions related to your situation you should speak with a local attorney.

Additional Drunk Driving Articles

Search LawInfo's Drunk Driving Resources