Field Sobriety Tests

Field sobriety tests are used to determine whether a person’s ability to operate a motor vehicle is impaired by alcohol and/or drugs. These tests measure coordination, attention, balance, agility, and the ability to follow instructions. Contrary to popular belief, a person does not pass or fail a field sobriety test. Rather, the officer makes notes of visible signs of impairment during the motorist’s performance of each test. In California, the most common field sobriety tests include:

  • Horizontal Gaze Nystagmus – HGN (follow an object with your eyes)
  • Walk and Turn (walking in a straight line)
  • One Leg Stand (raising one leg for 30 seconds)

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.

A person who is impaired by alcohol will have difficulty smoothly tracking a moving object. In the HGN test, the officer observes a suspect’s eyes as they follow a horizontally moving object (such as a pen). The officer looks for three indicators of impairment in each eye: 1. if the eye cannot follow a moving object smoothly, 2. if jerking is distinct when the eye is at maximum deviation, and 3. if the angle of onset of jerking is within 45 degrees of center.

If the officer observes four or more clues in the suspect’s eye(s), he or she likely has a blood alcohol concentration of 0.10% or more. The research indicates that this test allows proper classification of approximately 77 percent of suspects. HGN may be present if the person has consumed seizure medications, phencyclidine, various inhalants, barbiturates, and other depressants.

Divided Attention Testing

The walk-and-turn test and one-leg stand test are “divided attention” tests. 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.

The above three tests have become known across America as the “Standardized Field Sobriety Tests” (SFST). Many studies have shown that the above tests may be only 65%-80% accurate. Therefore, if these tests were used to convict people of DUI, 20% to 35% would be wrongfully convicted.

There are also several factors that can affect how well a DUI suspect performs on any of the field sobriety tests. Among these factors are: poor instructions, fatigue, injuries, intimidation, weight, natural coordination, weather conditions, and nervousness. Each test’s degree of difficulty may also impact a person’s performance. It is also important to note that even a sober person could have difficulty passing field sobriety tests.

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.

If you were recently arrested for DUI, it is important that you consult with an experienced California DUI lawyer. Although many experienced attorney’s handle DUI cases, it is important to find an expert DUI lawyer who has a wealth of DUI experience to properly evaluate your case. At California Criminal Defense Center, you are guaranteed representation by a highly skilled DUI lawyer who will take the time to explain the process to you and fight hard to obtain optimum results in your case.

To schedule a confidential and free consultation with a skilled DUI lawyer at California Criminal Defense Center, you can call us toll free at 1-800-DUI-KING (1-800-384-5464), or you may email us by completing the free case evaluation form.