The Standardized Field Sobriety Test are 3 tests administered by an officer during a traffic stop in order to determine if a driver is impaired.
The three most common standardized sobriety tests, are:
Horizontal gaze nystagmus is an involuntary jerking of the eyeball which occurs 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 and sustained nystagmus when the eye is at maximum deviation, or if the angle of onset of jerking is prior to 45 degrees of center. The subject is likely to have a BAC of 0.08 or greater if, between the two eyes, four or more clues appear. A 1998 validation study found that this test allows proper classification of approximately 88 percent of subjects. HGN may also indicate consumption of seizure medications, phencyclidine, a variety of inhalants, barbiturates, and other depressants.
The walk-and-turn test:
The subject is directed to take nine steps, touching 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 eight 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, steps off the line, takes an incorrect number of steps, or makes an improper turn. A 1998 validation study found that 79 percent of individuals who exhibit two or more indicators in the performance of the test will have a BAC of 0.08 or greater.
The one-leg stand test:
The subject is instructed to stand with one foot approximately six inches off the ground and count aloud by ones beginning with one thousand (one thousand-one, one thousand-two, etc.) until told to put the foot down. The officer times the subject for 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. A 1998 validation study found that 83 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.
There are many factors that might render a person unable to successfully complete one or more of the SFSTs. For instance, regarding the HGN test, the person asked to consent to such a test might be suffering from an eye disease or condition that affects his/her ability to see and consequently confound the test and results. Age, injury or disease could also affect the ability of a person to perform the one-leg stand test or the walk and turn test. As a general rule, an officer should ask the DUI suspect whether they can give any reason why they cannot perform the test and their answer should be carefully noted in the officer’s report. Other disabilities, such as deafness, should be taken into consideration and noted as well.
The three most common standardized sobriety tests, are:
- Horizontal Gaze Nystagmus (HGN) Test
- Walk-and-Turn Test
- One-Leg Stand Test
Horizontal gaze nystagmus is an involuntary jerking of the eyeball which occurs 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 and sustained nystagmus when the eye is at maximum deviation, or if the angle of onset of jerking is prior to 45 degrees of center. The subject is likely to have a BAC of 0.08 or greater if, between the two eyes, four or more clues appear. A 1998 validation study found that this test allows proper classification of approximately 88 percent of subjects. HGN may also indicate consumption of seizure medications, phencyclidine, a variety of inhalants, barbiturates, and other depressants.
The walk-and-turn test:
The subject is directed to take nine steps, touching 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 eight 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, steps off the line, takes an incorrect number of steps, or makes an improper turn. A 1998 validation study found that 79 percent of individuals who exhibit two or more indicators in the performance of the test will have a BAC of 0.08 or greater.
The one-leg stand test:
The subject is instructed to stand with one foot approximately six inches off the ground and count aloud by ones beginning with one thousand (one thousand-one, one thousand-two, etc.) until told to put the foot down. The officer times the subject for 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. A 1998 validation study found that 83 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.
There are many factors that might render a person unable to successfully complete one or more of the SFSTs. For instance, regarding the HGN test, the person asked to consent to such a test might be suffering from an eye disease or condition that affects his/her ability to see and consequently confound the test and results. Age, injury or disease could also affect the ability of a person to perform the one-leg stand test or the walk and turn test. As a general rule, an officer should ask the DUI suspect whether they can give any reason why they cannot perform the test and their answer should be carefully noted in the officer’s report. Other disabilities, such as deafness, should be taken into consideration and noted as well.
