DUI Prosecution and Field Sobriety Tests

During a DUI prosecution, the prosecution team, made up of the arresting officer, the prosecuting lawyer, and a DUI criminalist, will attempt to use the results of field sobriety test (FSTs) to prove that you are guilty of drunk driving.

Testimony will likely include statements alleging that you performed poorly on these tests and were not able to follow “simple” instructions given by the officer. When you retain a good DUI defense lawyer, he will attempt to show that your nerves, natural physical coordination, and several other issues drastically affected your ability to perform these balance and coordination tests. In addition we will get the arresting officer to admit that you successfully completed the FSTs and attempt to prove that the number of things you successfully completed far outweighs the tasks you did not complete successfully. This helps to show the officer’s bias towards you. With 25 years experience, Mr. Devitt is certainly a qualified DUI defense lawyer for your potential success fighting a DUI charge.

In addition the actual field sobriety tests that you were made to perform by the officer will likely be questioned. Many officers do not administer the NHTSA 3 Standardized Field Sobriety Tests and often times, when they do administer the correct tests, they do not administer them properly or evaluate them correctly.

The approved field sobriety tests for a California DUI are:

  1. Horizontal gaze nystagmus test: involves following an object with the eyes (such as a pen) to determine characteristic eye movement reaction.
  2. Walk-and-turn (heel-to-toe in a straight line): This test is designed to measure a person’s ability to follow directions and remember a series of steps while dividing attention between physical and mental tasks.
  3. One-leg-stand.

Other, non-scientifically validated test, include:

  1. Modified-position-of-attention: feet together, head back, eyes closed for thirty seconds; also known as the Romberg test.
  2. Finger-to-nose: tip head back, eyes closed, touch the tip of nose with tip of index finger.
  3. Recite part of the alphabet, sometimes backwards!
  4. Finger counting: touch each finger of hand to thumb counting with each touch (1, 2, 3, 4, 4, 3, 2, 1)
  5. Count backwards from a number ending in a number other than 5 or 0 and stopping at a number ending other than 5 or 0. The series of numbers should be more than 15.

Studies by the National Highway Traffic Safety Administration (NHTSA) explain that these FSTs are not designed to detect actual impairment, but are only intended to show likelihood that a driver is at or above a blood alcohol content of 0.08%. Additionally, further independent studies shed a fair amount of doubt on the usefulness of these tests. A 1991 study by Dr. Spurgeon Cole of Clemson University attempted to study the accuracy of FSTs. He taped participants, all of whom had a BAC of 0.00%, performing six common field sobriety tests and subsequently showed these tapes to 14 police officers. The officers were not informed of the participants’ BAC, and they were asked to determine, based on the tapes, whether or not the participants had “had too much to drink and drive” (sic). The officers suggested that 46% of the participants, who all had no alcohol in their system, were too impaired to drive. This study clearly demonstrates the possible inaccuracies of FSTs.

One extremely common FST used by many officers in the portable breathalyzer. This small, inexpensive unit, often called a preliminary alcohol screening (PAS) or preliminary breath test (PBT), is actually a less sophisticated version of the breathalyzer unit which is administered at police stations. The breathalzyers at the police stations use infrared spectroscopy to determine BAC while the PAS units use much simpler electrochemical technology. The PAS units are not intended to be used in court as evidence of actual BAC; they are only intended to be used to determine probable cause for arrest. The DUI Genius will cite past studies, new evidence, and improperly administered field sobriety tests during your trial to help show that you were not impaired the time of your arrest.

Understanding Potential Field Sobriety Tests


In California, the one-leg stand field sobriety test is very common and you can expect to perform this is you are pulled over on suspicion of DUI. Research has shown that if a suspect exhibits two of the four “clues” (discussed below) that there is a 65% chance of the suspects BAC being 0.10% or higher. When this test is administered, the suspect is instructed to stand with both legs together, select either their right or left leg, lift it approximately 6 inches off the ground, and count off by thousands. While you are performing this task, the officer is looking for clues that could indicate impairment which include:

  1. The use of arms for balance
  2. Hopping
  3. Swaying
  4. Putting your foot down during the test

This test can only be performed for 30 seconds. If the officer notices two of the four clues they will very likely request a breathalyzer test. The test is not easy for sober drivers or anyone with a balance problem.


Another extremely common test is the Walk and Turn test. This is a popular test because it measures a subject’s ability to divide their attention and it is often perceived as very simple. During this test your will be instructed to place your right foot directly in front of your left in a heel-to-toe position. Your arms must remain at your side and you are instructed to walk on a line, nine steps forward, turn on one foot 180 degrees, and walk nine steps forward. The officer is looking for two of the eight clues that you may be impaired. The clues for this test include:

  1. Unsteady balance
  2. Starting too soon, before the officer instructs you to start
  3. Delayed walking
  4. Not touching the heel to the toe
  5. Stepping off the line
  6. Raising your arms for balance
  7. Improper turning
  8. Incorrect amount of steps

Some research shows that if the subject shows two of the eight clues there is a 68% chance of having a BAC above 0.10%. Our experts can dispute this!


Horizontal gaze nystagmus is the involuntary jerking or twitching of the eye as it moves from center towards the far right or left sides. According to research the jerking movements become more pronounced as the driver becomes more impaired. This has shown the most reliability in determining the sobriety of a driver; if the subject fails the test there is a 77% chance that the driver has a BAC of 0.10% or higher. When administering this test the officer will hold a pen, pencil, or some other object in front of the subject and instruct them to follow it with their eyes as the officer moves it from right to left. The officer is looking for three clues to impairment, including:

  1. Are the eyes smoothly following the object?
  2. Is nystagmus present at the extremes?
  3. Is the angle of onset 45 degrees or less?

Should you take the tests?

All FSTs are completely voluntary. There is no statute that requires a person who is suspected of a California DUI to perform field sobriety tests. Under California law, every person has the right to remain silent and not to incriminate themselves. It is not and should not be considered a form of “consciousness of guilt” for a person to refuse to perform any voluntary test, including a voluntary field sobriety tests offered by a California DUI police officer. You always have the right to refrain from performing field sobriety tests and this does not prove your guilt unless you are under 21 or on probation for a DUI. That being said, exercising your right to opt out of field sobriety tests may be considered by the officer in determining probably cause for arrest. Your DUI defense lawyer will take into account all of your actions as well of those arresting officer when attempting to show the court your innocence.

Refusing field sobriety tests is not the same as refusing required chemical tests, which include blood or implied consent breath tests. Refusing these tests can be a statutory refusal and can be considered as “consciousness of guilt”. There are plausible reasons for refusing the test however, which include: officer-induced confusion and interference with the person’s ability to hear and understand the officer’s required chemical test refusal admonition.

A California DUI police officer should admit:

  1. There is no California Vehicle Code section that requires field sobriety tests
  2. There is no California Penal Code section that requires FST’s
  3. There is no law that requires a person to do FST’s
  4. If an officer would be suspected of a California DUI, the officer could exercise his right to not perform these tests

Why California Field Sobriety Test Results Are Often Unreliable

The first reason FST results can be unreliable is because even a person who is completely sober, especially someone with certain medical conditions, can fail these tests. Many factors including age, weight, gender, illness, and stress can affect your balance and concentration, and thus, your performance on a field sobriety test. Additionally, other factors outside of your control can affect your performance like: wet or slippery surfaces, cold or windy weather, or even unstable footwear like heavy boots or tall heels. All of these factors can combine together to create inaccurate results on a FST.

Research funded by the National Highway Traffic Safety Administration (NHTSA) resulted in the adoption of the so-called “standardized” field sobriety tests. A study completed in 1997 determined that the most effective field sobriety tests were the one-leg stand, the walk-and-turn, and the horizontal gaze nystagmus tests. But, even using these, the most effective FSTs, research showed that 47% (nearly half) of the participants who failed the tests actually had BAC concentrations that were less than the legal limit. Burns and Moskowitz, Psychophysical Tests for DWI Arrest: Final Report, DOT-HS-802-424, NHTSA (1977).

Field sobriety tests are largely unknown or unfamiliar to most people and so they are unpracticed which can significantly increase the difficulty for the people asked to perform them. Additionally the margin of error is extremely slim for these tests; as few as two clues can cause an individual to be classified as an impaired driver when the true reason may simply be unfamiliarity with the test.

Further research was conducted in 1986 and was reported in Halperiri, Is the Driver Drunk? Oculomotor Sobriety Testing, 57 Journal of the American Optometer Association 654 (1986). The research was designed to determine the tests’ ability to show whether a suspect’s BAC was above or below the legal limit, rendering the driver “impaired”. The research was conducted under strict laboratory conditions and showed that the walk-and-turn test returned a correct assessment 75.1% of the time, a one-leg-stand test proved correct 75.5% of the time, and the nystagmus test 81.8% of the time. When all three tests were given together a correct identification was gathered 83.4% of the time. While these numbers may seem high, think of the results in reverse; this means that FSTs identify approximately one fourth of innocent suspects as guilty. Also remember these tests were performed under ideal conditions with experienced, accurate administrators.

The federally funded researchers from the Southern California Research Institute published the findings of their research in 1987. An article entitled Sobriety Tests for the Presence of Drugs, 3(1) Alcohol, Drugs and Driving 25 (1987), came to the conclusion that field sobriety tests do not accurately measure driving impairment. The researchers agreed such tests determine balance, reaction time, and steadiness but came to the conclusion that a connection between these factors and driving ability “is not apparent since neither a steady stance nor simple movement time is essential to the safe operation of a motor vehicle.” The researchers came to a final conclusion that while the FSTs may help to indicate a presence of alcohol, the tests may not necessarily measure driving ability

Going back to the research conducted by Dr. Spurgeon Cole in 1991, it has been shown that field sobriety tests are barely better than a coin flip at predicting intoxication in driver. A staggering 46% of the participants, all of whom had a BAC of exactly 0.00%, were determined by officers to be unable to safely operate a motor vehicle. Cole & Nowaczyk, Field Sobriety Tests: Are They Designed for Failure?, 79 Perceptual and Motor Skills 99 (1994).



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