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Field Sobriety Tests

For persons accused of DUI in California, Field Sobriety Tests are generally used to determine if a person has been driving while intoxicated, and whether or not there is probable cause to arrest the driver for DUI. 

Most drivers are not aware that there are only three recognized field sobriety tests. The Standardized Field Sobriety Test (SFST) is a battery of three tests administered and evaluated in a standardized manner to obtain validated 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. A formal program of training was developed and is available through NHTSA to help police officers become more skillful at detecting DUI suspects, describing the behavior of these suspects, and presenting effective testimony in court. Formal administration and accreditation of the program is provided through IACP. Unfortunately, many officers either did not attend the formal training, or relax the strict standards of the three tests, sometimes adding tests that are not recognized. 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.

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.

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 on one foot 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. NHTSA research indicates that 68 percent of individuals who exhibit two or more indicators in the performance of the test will have a BAC of 0.10 or greater. In the one-leg stand test, the suspect is instructed to stand with one foot approximately six inches off the ground and count aloud by thousands (One thousand-one, one thousand-two, etc.) until told to put the foot down. The officer times the subject for a 30 seconds. The officer looks for four indicators of impairment, including swaying while balancing, using arms to balance, hopping to maintain balance, and putting the foot down. NHTSA research indicates that 65 percent of individuals who exhibit two or more such indicators in the performance of the test will have a BAC of 0.10 of greater. The effectiveness of SFST in court testimony and evidence depends upon the cumulative total of impairment indicators provided by the three-test battery. The greater the number of indicators, the more convincing the testimony. Because SFST is administered according to national standards and is supported by significant research, it has greater credibility than mere subjective testimony.

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 such as a pen or small flashlight, horizontally with his 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. If, between the two eyes, four or more clues appear, the suspect likely has a BAC of 0.10 or greater. NHTSA research indicates that this test allows proper classification of approximately 77 percent of suspects. HGN may also indicate consumption of seizure medications, phencyclidine, a variety of inhalants, barbiturates, and other depressants.

Testing Accuracy:
The NHTSA manuals (plural here, because 6 separate versions have now been released) say 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.

Knowledgeable criminal defense lawyers know that 98% 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. 

Also, recent research and scientific review of the testing protocols and scoring methodology have brought the NHTSA “Standardized Field Sobriety Tests (“SFSTs”) into serious question.  More and more courts are now saying “no” to these questions. In a recent New Mexico case, a high-level court has declared that the person who “developed” the tests (Dr. Marcelline Burns) was not qualified to testify as an expert witness about the scientific principles behind the HGN test. (Lasworth v. State, 42 P.2d 844 (N.M. App. 2001).

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. Several appellate court decisions have indicated that, if you administer a test that requires the subject to respond orally in other than a routine information-giving fashion, such as requiring them to indicate the date of their sixth birthday, and if they are in custody at the time, you should administer the Miranda warning first, because you are seeking information from them that is testimonial or communicative in nature.

Tests given by some officers may include reciting the alphabet (or a portion thereof), picking up coins off the ground, patting or hand clapping, estimating time, counting backwards, reciting the alphabet, 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. Some have in the past involved strange, one-legged tapping on the roadway with a raised foot. These “made-up” tests were administered to subjects without any scientific or empirical basis for reliability in detecting an impaired driver. These tests were designed for failure, not for fairness.  Even worse, police officers often forced people to perform these voluntary evaluations, thereby violating these citizens’ rights.

Some “non-standardized” tests are so ridiculous and difficult that proof of non-validity was easy with almost any jury or judge. 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 criminal defense attorney who knows the “limitations” of these field tests.

The Voluntary Nature of FST Tests:
Recognize that these tests are completely voluntary. These voluntary “tests” (yes, voluntary) are developed 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 DUI / 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 defense attorney know as much or more about these tests as the police, if he or she is going to defend you. 

DUI defense counsel usually challenges 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. By comparison, polygraph (lie detector) tests are more than 90% accurate when conducted by a qualified operator), and (absent a stipulation by both parties) are still not permitted into evidence by most courts.

Roadside Alcohol Screening Tests:
A portable breath testing device may be used by police officers in determining whether or not a motorist is under the influence of alcohol. California had previously banned the use of these voluntary “non-evidential” screening devices for use at trial, but allows it at a pre-trial hearing at which “probable cause” for arrest is involved.

Like other “field tests”, these devices are used at the roadway. Often, police officers do not regularly check the devices for calibration.  Furthermore, the manufacturer’s instructions (e.g., failing to observe a 15 minute deprivation period, waiting at least 4 minutes between tests, or clearing the prior test results) for proper use are routinely ignored. California’s Administrative Code, Title 17, contains all the information necessary for what constitutes a valid blood or breath test.

Some police agencies try to use these roadside testers as evidential tests. This is accomplished when a small printer is attached to the breath test apparatus. Unless your jurisdiction uses such a device as an official state-mandated breath test, no person should ever submit to these devices and risk a false positive result and almost certain arrest.  Politely decline to give this voluntary sample, although be aware that refusal of an official breath or blood test later can be considered a refusal, triggering a license revocation.

If you have any other questions, make sure you speak with, visit, or email a qualified attorney.

Information on Orange County Drinking and Driving.
Information on San Diego Drinking and Driving.

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