Field Sobriety Testing




Drivers suspected of DUI will be asked by police officers to perform a battery of roadside tests known as Field Sobriety Tests (FSTs). Virtually all DUI prosecutions will use the results of these tests in court. The only purpose these tests have is to try to try to convict you of DUI. These voluntary tests were developed by police to help them determine whether or not a suspect is under the influence of alcohol or drugs. On the surface, these tests appear to be objective, scientific, and reliable. On the surface, it may seem that most sober people can perform these tests with no difficulty. It is Mr. Yeargan’s job to dispel these myths, and show the jury that these tests are not reliable so that they will not erroneously convict you. Being trained in Standardized Field Sobriety Testing, having trained officers, and preparing a vigorous cross examination of the arresting officers are several of the attacks Mr. Yeargan will use to defend you at trial.

Remember, the Field Sobriety Tests are voluntary tests. You are under no obligation to perform them. I, along with any other good defense attorney, tell my friends and family never to attempt these tests because they are designed to fail and they are wholly unreliable.

Only three tests have been “scientifically” studied, and declared to have any reliability in helping officers determine if a motorist’s blood alcohol level is above the legal limit. The limit used in these tests was .10 grams percent. In 1977, the Southern California Research Institute began research for the National Highway Transportation Safety Association (NHTSA) to determine which tests being used by law enforcement agencies yielded the most accurate results of whether not a motorist is under the influence of alcohol. The other objective of this research was to develop and standardize tests that would produce the most reliable evidence of impairment. After years of federal research, three tests would ultimately be classified as “Standardized Field Sobriety Tests” (SFTS) and would be sanctioned by NHSTA in 1984. These tests are the One Leg Stand Test, The Walk and Turn Test, and the Horizontal Gaze Nystagmus Test.

In promulgating these standardized evaluations, NHTSA has created exacting standards and guidelines that must be followed to ensure the accuracy and reliability of these tests. Every officer who is NHTSA trained receives a manual which sets forth these exacting guidelines and procedures which are required to ensure the validity of FSTs when they are administered to DUI suspects. However, the manuals state that if these tests are not performed properly, or are administered without adhering to the strict NHTSA guidelines and training procedures, such actions will compromise the validity of the evaluations.

Beginning in the 1970’s, NHTSA began studies to determine if there was a correlation between tests that were being given by officers in the field and if a driver who had been drinking had a blood alcohol content of 10 grams percent or higher. NHTSA used 238 volunteers, and subjected them to the Finger to Nose Test, Counting, One Leg Stand, Walk and Turn, Finger Count, Tracing, Horizontal Gaze Nystagmus, Reciting the Alphabet, and Picking Up Coins Test. NHTSA concluded that only 3 tests had a better than 50/50 percent chance of indicating that a driver’s BAC level was .10% or higher. These tests were not designed to determine whether a driver is under the influence of alcohol, but only to determine if a driver’s BAC is .10% or higher.

The One Leg Stand Test
    The One Leg Stand Test, when conducted properly on a qualified subject on a level and dry surface yields a 65% accuracy rate when demonstrated and scored properly. Conversely, this means there is also a 35% chance of a false positive. Before the suspect performs the One Leg Stand Test, the officer must give the following precise instructions and demonstration:
  • Instruct the subject to stand with their feet together, and place their hands at their sides;
  • Instruct the subject not to begin the test until the officer instructs them to;
  • Ask the subject if he/she understands;
  • Instruct the subject to stand on either leg of their choosing while keeping the other leg six inches off the ground with their toes pointed forward and keeping their foot parallel to the ground;
  • The officer must now demonstrate the stance;
  • Instruct the subject to count out loud “One thousand one, One thousand two,” until the officer instructs them to stop;
  • The officer again demonstrates the stance and the count;
  • Ask the subject if he/she understands;
  • Instruct the subject to begin the evaluation;
  • If the subject places their foot down or interrupts the test allow them to continue uninterrupted, without restarting the count at “one thousand one,” until the officer instructs the subject to stop


    During this evaluation, the officer is looking for four clues of impairment:
  1. The subject puts his/her foot down
  2. The subject uses their arms for balance (raising them more than 6 inches from their sides).
  3. The subject sways.
  4. The subject hops.


These clues may be remembered by using the pneumonic PUSH (Puts foot down, Uses arms, Sways, Hops).

This test is to be scored objectively giving one point for each clue observed regardless of how many times the officer observes the clue. For example, if the subject places his/her foot down 4 times during the test the officer only gives one point for “Putting foot down.” A maximum of 4 clues is possible. The officer may only give points for the 4 clues that are established by NHTSA, however the officer is encouraged to make notes regarding any other indicia of intoxication that he notices during the evaluation. If a subject scores 2 or more clues on this evaluation he or she is said to fail the evaluation. This test is supposed to be scored objectively based on NHTSA standards and criteria, but many officers will arrest a suspect if the suspect does not perform the tests up to the officers own personal expectations regardless of what is required by NHTSA. Often, an officer will substitute his own impressions over the NHTSA criteria and arrest a DUI suspect regardless of their performance. When this is brought to the attention of the jury it is a powerful weapon in obtaining a “not guilty” verdict.

Factors which may interfere with the One Leg Stand test include: a test area that is not dry and level, footwear such as high heels, certain medical conditions, the subject being over the age of 65, and the subject being at least 50 pounds overweight.

The Walk and Turn Test

The Nine Step Walk and Turn evaluation, when conducted properly on a well qualified individual on a dry, level surface, has a 68% reliability rate. Again, this leaves a 32% chance for false positives. The Walk and Turn Test is divided into two parts: the instructional phase and the walking phase.

During the instructional phase the officer has the test subject stand with the heel of his right foot touching the toe of his left foot with his hands placed at his sides. The subject is to hold this pose while the officer gives the instructions for the Walk and Turn test. If the subject breaks this pose, or begins the test before the officer instructs him to begin, the subject is given a clue for either violation.

    The officer places the subject in the instructional phase by giving the following instructions:
  • I want you to stand with your right foot in front of your left, with your right heel touching your left toe;
  • Hold that position and keep your hands at your sides;
  • Do not begin the test until I instruct you to do so;
  • Do you understand?


    At this time the officer will begin to give the instructions for the rest of the test. Remember, the subject must stand heel to toe, arms at his side, and not start the test until he’s instructed to do so or he will be giving “clues” of impairment to the officer. The officer will then give the following instructions:
  • I want you to take a series of nine heel to toe steps;
  • As you walk, I want you to count each step out loud;
  • When you take your ninth step I want you to pivot on whichever foot your ninth step is on, take a series of small steps with the other foot to turn around, and then take nine steps back counting each step out loud.
  • At the same time as these instructions, the officer should be demonstrating these instructions, including the turn, as well.
  • As you walk, I want you to look down at your feet, count each step out loud, keep your hands at your sides, and don’t stop the test once you have started;
  • Do you understand?
During this test, the officer is looking for eight clues of impairment.

    During the instruction phase of the test, the officer is looking for two clues of impairment:
  1. The subject breaks heel to toe position.
  2. The subject starts the test too soon (before the officer instructs him to do so).


    During the walking phase of the test, the officer is looking for six clues of impairment:
  1. The subject stops while walking.
  2. The subject misses heel to toe while walking (by at least one half inch).
  3. The subject raises his arms six inches or more while walking.
  4. The subject steps off the line.
  5. The subject turns improperly.
  6. The subject takes the wrong number of steps.


The 6 clues during the walking phase can be remembered by using the pneumonic SHORTS (Stops walking, misses Heel to toe, steps Off line, subject Raises arms, improper Turn, wrong number of Steps).

Again, one point is given for each clue observed regardless of how many times the clue is observed. Just like the One Leg Stand, two or more clues on the Walk and Turn Test is considered failing.

Factors which may interfere with the Walk and Turn test are: wind, rain, darkness, highway traffic, uneven pavement, debris on the road, the subject’s footwear, the subject being over the age of 65, or the subject being more than 50 pounds overweight.

Horizontal Gaze Nystagmus (HGN)

The Horizontal Gaze Nystagmus (HGN) Test when performed properly on a medically qualified individual has a claimed 77% reliability rating. During the HGN evaluation the officer is looking for nystagmus of the eye. Nystagmus is simply the involuntary jerking of the eye. This involuntary jerking of the eye is often compared to the movement of windshield wipers on a dry windshield, or a marble on sandpaper.

    To properly administer this test the officer must:
  • Hold a stimulus (usually the officer’s finger, or pen) 12 to fifteen inches from the subject’s face);
  • Hold the stimulus slightly above the subject’s eye level;
  • Tell the subject to follow the stimulus with only their eyes making sure they hold their head completely still;
  • Move the stimulus smoothly in a straight line;
  • Initially, the officer must check each eye for equal pupil size, and equal tracking. This is done to see if the subject has suffered a concussion or has a glass eye;
  • The officer then checks each eye for 3 possibly clues;
  • The officer will check each eye twice for each set of clues.


    During this evaluation, the officer is looking for 6 clues of impairment (2 clues per eye):
  1. Lack of smooth pursuit;
  2. Distinct and sustained nystagmus at maximum deviation;
  3. Onset of nystgamus prior to 45 degrees.


Unless a subject has a glass eye, or a serious medical issue, an officer should never have an odd number of clues on the HGN evaluation. The officer should always have 2, 4, or 6 clues. Also, each set of clues is progressive. Therefore, an officer should never notice distinct and sustained nystagmus at maximum deviation without noticing a lack of smooth pursuit, or onset of nystgmus prior to 45 degrees without observing the other four clues.

Factors which may interfere with the HGN test are: the subject having an artificial eye, head trauma, the subject having damaged or weak vision, eye irritants such as wind, dust, and rain, and other distractions such as flashing police lights, traffic driving by, and other motorist’s headlights. Severe medical conditions such as brain tumors, and brain damage will effect the test as well. Also, some individuals have a natural nystagmus, and have a natural involuntary jerking of the eye.

Imperfect Results

In summary, the National Highway Safety Transportation Authority (NHTSA) would have us believe that cumulatively these 3 tests, if done correctly, have an 83% accuracy rate of indicating whether a subject has a BAC of .10% or more. Knowledgeable DUI attorneys know that 98% of officers conduct these tests incorrectly, or on unqualified or unapproved individual, or score them incorrectly. In some situations, officers make all 3 of these mistakes. When done incorrectly, these field sobriety tests have ZERO percent reliability. A good DUI lawyer will be able to cross examine the arresting officer using state, federal, and NHTSA approved materials, along with the attorney’s own training, to show the jury the officer was wrong.

Remember, NHTSA has admitted that under perfect testing conditions on medically qualified individuals that 35% of sober and drug free individuals show clues of impairment on the One Leg Stand test, 32% of sober subjects get flawed results on the Walk and Turn test, and 23% of sober subjects are said to be over .10% BAC on the HGN test. These inaccurate numbers are likely to be seen under perfect conditions, on perfectly healthy people, when the tests are performed perfectly. Remember, 98% of field sobriety tests are not given perfectly, under perfect conditions, on perfect people. According to the NHTSA manual, “if any one of the standardized field sobriety test elements is changed, the validity is compromised.” Therefore, your DUI case needs to be evaluated by an experienced, NHTSA certified, DUI attorney to determine where the police made mistakes that compromised the decision to arrest you.
Disclaimer Copyright 2006 Yeargan & Associates, All Rights Reserved.