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What is the purpose of the standardized field sobriety test?

Movies and television shows depict police officers making drunk drivers touch their noses, say the alphabet backwards and other tasks to determine whether they are intoxicated. In real life, these do not fall under the standardized field sobriety tests because their accuracy is highly questionable.

Instead, in the 1970s, a battery of three tests called the Standardized Field Sobriety Test was created. Supposedly, the accuracy of the SFST is high enough to provide probable cause to police for DUI arrests and evidence of impairment for prosecutors. Understanding the purpose of the tasks that make up the SFST comes in handy in defending you against drunk driving charges.

The one-leg stand test

While you stand on one foot for approximately 30 seconds, the officer is looking to see if you exhibit any of the following:

  • Swaying
  • Hopping
  • Putting foot down
  • Using arms for balance

A study done in 1998 concluded that exhibiting two or more of these behaviors coincided with a blood alcohol concentration of .10 or higher in 83 percent of the subjects.

The walk-and-turn test

While you take nine heel-to-toe steps in a straight line, turn 180 degrees on one foot and repeat the steps in the opposite direction, the officer looks for the following behaviors:

  • Failing to touch heel-to-toe
  • Failing to maintain balance
  • Using arms for balance
  • Failing to understand instructions
  • Failing to perform the test while listening to instructions
  • Taking the wrong number of steps
  • Failing to maintain a straight line
  • Halting walking in order to regain balance
  • Beginning the test before told to
  • Making the turn incorrectly

The same study indicated that exhibiting two or more of these behaviors equated to a BAC of .08 or higher in 79 percent of participants.

The horizontal gaze nystagmus

When you gaze to the side, your eyes jerk involuntarily. This is called horizontal gaze nystagmus, and everyone does it. Research indicates that drunk individuals exhibit HGN when they shouldn't. Your eyes should be able to follow an object smoothly unless something is wrong with them. An officer considers that you failed this test if the following occur:

  • Your eyes jerk following an object
  • Jerkiness begin before the 45 degree off-center mark
  • Jerking occurs at maximum deviation

The 1998 study found that 88 percent of those who failed this test had a BAC of .08 or higher.

The SFST isn't always accurate

There are times when the SFST fails to accurately predict intoxication. Numerous medical and physical conditions can cause you to fail the test. Even factors such as age and weight can affect the results. Some people naturally have balance issues that preclude them from passing the one-leg and walk-and-turn tests. Even the HGN test does not always indicate intoxication. People who take seizure medications, depressants and other drugs prescribed for medical conditions can fail this test.

For these reasons, you should never simply accept that a criminal court would find you guilty of DUI based on the SFST. A seasoned North Carolina DUI attorney will challenge the results of this battery of tests, along with other aspects of your case.

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