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Most drivers and surprisingly many police officers are unaware that there are only three recognized field sobriety tests. The Standardized Field Sobriety Test (SFST) is a battery of three tests used to detect indicators of impairment and establish probable cause for arrest. These tests were developed as a result of research sponsored by the National Highway Traffic Safety Administration (NHTSA) and conducted by the Southern California Research Institute. The three tests of the SFST are:
- The horizontal gaze nystagmus (HGN)
- The walk-and-turn
- The one-leg stand
These tests are administered systematically and are evaluated according to measured responses of the suspect.HGN Testing Horizontal gaze nystagmus is an involuntary jerking of the eyeball which occurs naturally as the eyes gaze to the side. Under normal circumstances, nystagmus occurs when the eyes are rotated at high peripheral angles. However, when a person is impaired by alcohol, nystagmus is exaggerated and may occur at lesser angles. An alcohol-impaired person will also often have difficulty smoothly tracking a moving object. In the HGN test, the officer observes the eyes of a suspect as the suspect follows a slowly moving object, often a pen or small flashlight, horizontally with his or her eyes. The examiner looks for three indicators of impairment in each eye: if the eye cannot follow a moving object smoothly, if jerking is distinct when the eye is at maximum deviation, and if the angle of onset of jerking is within 45 degrees of center. HGN may also indicate consumption of seizure medications, phencyclidine, a variety of inhalants, barbiturates, and other depressants.Divided Attention Testing: The walk-and-turn test and one-leg stand test are “divided attention” tests that are supposed to be easily performed by most sober people. They require a suspect to listen to and follow instructions while performing simple physical movements. Impaired persons have difficulty with tasks requiring their attention to be divided between simple mental and physical exercises.If instructed properly by the officer, In the walk-and-turn test, the subject is directed to take nine steps, heel-to-toe, along a straight line. After taking the steps, the suspect must turn in a series of small steps and return in the same manner in the opposite direction. The examiner looks for seven indicators of impairment: if the suspect cannot keep balance while listening to the instructions, begins before the instructions are finished, stops while walking to regain balance, does not touch heel-to-toe, uses arms to balance, loses balance while turning, or takes an incorrect number of steps.Testing Accuracy: The NHTSA manual says that if the FST tests are not performed properly, or if conducted without adhering to the training protocols, such actions “compromise” the validity of these evaluations.The HGN evaluation, when performed correctly on proper subjects, had a 77% “claimed” reliability rating. The Walk-and-Turn exercise, when conducted properly on a qualified subject on a dry, level surface, was found to be 68% reliable. The One-Leg-Stand exercise, when conducted properly, on a qualified subject on a level, dry surface and under proper instructions and where correctly demonstrated and scored, reportedly yields about 65% reliability. Cumulatively, if all are done correctly, up to 83% correlation to a BAC of 0.10% or more may be expected according to NHTSA.Knowledgeable DWI criminal defense lawyers know that 95% or more of the officers administering these evaluations do them wrong, or conduct them in a manner (or on a test subject) not approved by the SFST manual, or grade the evaluations improperly, as per the manual, or ALL OF THE ABOVE. When done incorrectly, these evaluations have ZERO predicted reliability.Alternative Testing Methods: Sometimes, an officer will encounter a disabled driver who cannot perform the SFST. In such cases, some other battery of tests such as counting aloud, reciting the alphabet, or finger dexterity tests may be administered.Tests given by some officers may include reciting the alphabet (or a portion thereof), estimating time, counting backwards, touching fingers to the thumb in a pattern set by the officer, or touching index fingers to the tip of the nose while the person’s eyes were closed and head tilted back.Today, officers who lack NHTSA training invariably cannot cite any studies or scientific research which “validated” their tests, the scoring (e.g., “pass” or “fail”) or their testing methods. Almost always, no scoring system is used on tests which do not adhere to NHTSA guidelines. If non-standardized tests are used, the number of errors that are required for a subject to fail is totally subjective with each officer. Hence, the untrained officer is usually an easy target for a skilled and knowledgeable DWI criminal defense attorney who knows the “limitations” of these field tests.The Voluntary Nature of FST Tests: These voluntary “tests” (meaning you are in no way required to, and in most instances because of the officers lack of skill and training such tests can hurt you even though you may not be impaired as you will see below) are developed by NHTSA and implemented by police agencies to assist law enforcement officers in making roadside determinations as to whether a motorist is under the influence of alcohol or drugs. Through the performance of these tests or evaluations, the officer subjectively determines how the motorist reacts to and performs the requested tasks.Almost EVERY knowledgeable DWI attorney will say to you, “NO. Don’t attempt ANY ‘field tests’ — EVER.” That is because many studies have concluded that the SFSTs are “designed to fail” even sober drivers.A motorist's alleged poor performance on field evaluations may provide the “probable cause” (legal justification) an officer needs to arrest a person for impaired driving and may also become part of the proof used to later convict the person at trial. Therefore, it is very important that, in defending you, your DWI defense attorney know as much or more about these tests as the police.DWI defense attorneys usually challenge the subjective nature of the evaluations, the accuracy of the principles behind the tests, the accuracy of the administration of the tests, the credibility of the officer who “requested” the tests, and challenge all circumstances connected with the evaluations. An attorney representing you must attack the factual and legal issues that may arise regarding the officer's scoring and evaluation of the field tests.The reason that most credible scientists across America (and in other countries) are unwilling to categorize field tests — even NHTSA's tests — as being “scientific” is that too many variables are involved in roadside testing to ever eliminate pure chance and non-controlled circumstances from the equation (e.g., environmental conditions such as lighting and roadway slope).Even NHTSA admits that under optimal conditions (i.e., in an air-conditioned, well lighted room) 35% of sober, drug-free subjects get inaccurate results on the one leg stand test, 32% of sober subjects get flawed results on the walk and turn, and 23% of sober subjects are inaccurately said to be “over the legal limit” on the horizontal gaze nystagmus test. Roadside Alcohol Screening Tests: A portable breath testing device or PBT may be used by police officers in determining whether or not a motorist is under the influence of alcohol. Texas has not recognized the use of these screening devices for use at trial.Like other “field tests”, these devices are used on the roadside. Often, police officers do not regularly check the devices for calibration. You should never submit to these devices and risk a potentially false positive and/or inaccurate result and almost certain arrest. Politely decline to give this voluntary sample.To learn more about Field Sobriety Tests and DWI defense contact Mr. Shaw, an experienced DWI attorney at (214)726-0088.
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Field Sobriety Testing
