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Field Sobriety Tests

If an officer suspects you of driving under the influence of alcohol, part of his or her DUI investigation will often include a series of “field sobriety tests.” Field sobriety tests are a series of mental and physical tasks which law enforcement claims aids them in determining impairment. Although these tests are completely optional under California law, many people willingly submit to them out of fear of arrest, confusion of the law and a desire to be cooperative with law enforcement.

Contrary to popular belief, field sobriety tests are not “Pass or Fail” tests that you can simply pass and be on your way. In fact, by the time the officer gets to the field sobriety test portion of his DUI investigation, he most likely has already decided to arrest you regardless of how you perform on the test. Rather, the field sobriety tests are likely being used by the officer as a way to prop up their decision to arrest you, in case it is challenged in the future, such as in your court proceedings.

Consequently, if your officer made any mistakes in conducting the FSTs an attorney trained and certified in conducting field sobriety tests can dissect what they did wrong and begin to unravel the officer’s entire basis for the arrest.


Although an officer may subject you to a myriad of field sobriety tests during a DUI investigation, only three tests have been approved by the National Highway Traffic Safety Administration (NHTSA), which include the Horizontal Gaze Nystagmus test, the Walk and Turn test and the One Leg Stand test. NHSTA claims that when conducted properly, these three tests have been shown to be a reliable means to detect cues of impaired drivers based on various field studies. However, if you keep reading you will notice that NHTSA’s most reliable tests range between 65% and 77%, which would be between a D grade and a C+ grade on a test.

Horizontal Gaze Nystagmus (HGN) Test

NHSTA claims that the HGN test is the most reliable SFST. (See DUI Detection and SFST Participant Manual, 10/2015 citing a 77% accuracy at detecting subjects at or above 0.10 BAC.)

“Nystagmus” is an involuntary jerking of the eyes, which NHSTA claims is caused by alcohol and certain other drugs. Horizontal Gaze Nystagmus is an involuntary jerking occurring as the eyes gaze towards the side.

During this test, the officer will instruct you to follow the tip of his finger or a pen with your eyes to observe whether or not three clues are present in each eye: 1) lack of smooth pursuit, 2) distinct and sustained nystagmus at maximum deviation and, 3) onset of nystagmus prior to 45 degrees.

Walk and Turn Test

NHSTA claims that dividing a person’s attention between a task of listening, understanding and physically performing instructions can reliably predict impairment. NHSTA claims that the walk and turn test is the most reliable “divided attention” test. (See DUI Detection and SFST Participant Manual, 10/2015 citing a 68% accuracy at detecting subjects at or above 0.10 BAC.)

During the walk and turn test, the officer instructs you to take nine heel-to-toe steps forward and back, usually on an imaginary line. (Think of combining the game “Simon Says” with a choreographed dance routine that you aren’t allowed to practice. Good luck!)

Any deviation from following the instructions, i.e. (starts too soon, incorrect number of steps, improper turn) and any inability to physically perform the test, i.e. (cannot keep balance while listening to the instructions, stops while walking, does not touch heel to toe, steps off line, uses arms to balance) will be used as a cue of your impairment.

One Leg Stand Test

The one leg stand test is another SFST that NHSTA claims that can reliably predict impairment. (See DUI Detection and SFST Participant Manual, 10/2015 citing a 65% accuracy at detecting subjects at or above 0.10 BAC.)

During the one leg stand test, the officer instructs you to lift one leg approximately six inches off the ground (think the final scene of the movie “Karate Kid”) and count out loud while holding that position under instructed to stop. During this test the officer is looking for clues of impairment including whether the subject: sways while balancing, uses arms to balance, hops and/or puts their foot down.

NHSTA claims that a person with a BAC above .10 can rarely maintain there balance as long as 30 seconds.


If you are subject to a DUI investigation, depending on the law enforcement agency and individual officer, you may be subject to several non-standardized field sobriety tests, i.e. tests with absolutely no basis in research. Common non-standardized field sobriety tests are the: 1) Rhomberg/Modified Rhomberg Balance test, 2) Finger-to-Nose test, 3) Finger Count test, and 4) Hand Pat test. You may also be subject to a Preliminary Alcohol Screening (PAS) test, which is a pre-arrest breath test used by the officer to confirm suspicions of impairment.


Even if administered perfectly, NHSTA’s own studies show that these tests are unreliable, with their most reliable test topping out at 77%!. However, even if we assumed the tests were reliable, there are numerous variables that could further compromise the reliability any particular test, including: 1) improper administration by the officer, 2) physical disabilities not related to alcohol impairment, 3) mental disabilities not related to alcohol impairment, 4) improper surface conditions, 5) improper sound conditions, 6) improper lighting conditions, 7) improper clothing and/or footwear.

Kevin Fard, Esq. completed certification for the National Highway Traffic Safety Administration (NHTSA) & The International Association of Chiefs of Police (IACP) DWI Detection & Standardized Field Sobriety Testing which is the same training course law enforcement must complete to conduct Standardized Field Sobriety Tests.

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