Sobriety testing as evidence
Sobriety testing is a critical process used by law enforcement to assess whether individuals are intoxicated, particularly in situations where intoxication poses a danger, such as driving. The results of these tests often serve as key evidence in legal proceedings involving charges like driving while intoxicated (DWI) or driving under the influence (DUI). Various testing methods exist, including urine and blood tests, but field sobriety tests are commonly employed during traffic stops due to their convenience for on-site assessments.
The National Highway Traffic Safety Administration (NHTSA) has established the Standardized Field Sobriety Test (SFST), which includes three key assessments: the horizontal gaze nystagmus test, the one-leg stand test, and the walk-and-turn test. These tests are designed to evaluate an individual’s physical and cognitive abilities, with research indicating they can accurately determine intoxication over 90% of the time when used together. Additionally, after field tests, officers may conduct a breath test to ascertain blood alcohol content (BAC), with a legal threshold of 0.08% in most states, except Utah, where it is lower at 0.05%. Understanding sobriety testing is essential for recognizing its implications in public safety and legal contexts.
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Subject Terms
Sobriety testing as evidence
DEFINITION: Measures taken by law-enforcement officials to determine whether persons are intoxicated in situations in which being intoxicated is dangerous or unlawful.
SIGNIFICANCE: The results of sobriety testing by police officers are often used as evidence in court and may be the primary evidence in cases involving charges such as driving while intoxicated or driving under the influence of alcohol or other drugs.
Many different kinds of testing can reveal the presence or absence of intoxicating substances in the human body. Urine and blood tests can effectively screen for the presence of drugs or alcohol in a person’s system, but these tests are not generally convenient for providing information in the field when a law-enforcement officer suspects that someone may be under the influence. Instead, especially during traffic stops, field sobriety tests are used.
A law-enforcement officer may administer a field sobriety test any time the officer has reason to believe that a driver may be intoxicated. Among the many signs that indicate an individual may be under the influence of alcohol are the smell of alcohol on the breath, intoxicated demeanor, and slurred speech. These signs, however, are subjective. To increase the standardization of field sobriety testing across the United States, the National Highway Traffic Safety Administration (NHTSA) created the Standardized Field Sobriety Test (SFST), a set of recommended field test procedures.
The SFST consists of three separate tests, the results of which the administering officer evaluates on a variety of factors. The first test is designed to measure the subject’s horizontal gaze nystagmus (HGN), which is the jerking of the eye that occurs when the eye moves from one side to the other. This occurs naturally and cannot be controlled voluntarily. During the HGN test, the officer asks the subject to follow the movement of a small object, such as a finger or pen, with his or her eyes. The officer moves the object horizontally in front of the subject’s face and assesses the individual’s ability to follow the object as well as the amount and location of the jerking movements of the eyes. Compared with a person who is not intoxicated, a person who is intoxicated will show more jerking movement when the gaze is more centered.
The other tests in the SFST are the one-leg stand test and the walk-and-turn test. Both are designed to test the subject’s ability to do two or more things at the same time. During the walk-and-turn test, the officer asks the subject to take nine steps, heel to toe, in a straight line and then turn and take nine steps back. During the one-leg stand test, the subject attempts to stand on one leg while counting. During both of these tests the officer uses a predetermined set of guidelines to assess the subject’s ability to perform the specified tasks. The subject’s failure on a set number of attributes can result in a determination that the subject is intoxicated. Research has shown that officers who use the three tests of the SFST together make correct determinations of intoxication in more than 90 percent of cases.
After administering a field sobriety test, a police officer must gauge the suspect’s blood alcohol content, or BAC. An officer can administer a portable breath test at the scene, but while these can be used as a guide, they are not admissible in court. If an officer believes that a person may be intoxicated, he or she can submit the suspect to a more accurate chemical breathalyzer test or a blood test to determine BAC. As of 2024, in all states except Utah, a person was considered to be legally intoxicated if their blood alcohol level was 0.08 percent or above. In Utah, the level was 0.05 percent. This level is sometimes referred to as being “legally drunk,” although it only represents the level at which police can definitively charge a person with driving under the influence (DUI). If a person’s level is under 0.08, an officer can still charge them with DUI depending on the circumstances.
Bibliography
Haggin, Daniel J. Advanced DUI Investigation: A Training and Reference Manual. Springfield, Ill.: Charles C Thomas, 2005.
"SFST Instructor Guide." National Highway Traffic Safety Administration, February 2023, www.nhtsa.gov/sites/nhtsa.gov/files/2023-03/15911-SFST‗Instructor‗Guide‗2023-tag.pdf. Accessed 16 Aug. 2024.
Wilson, Mike, ed. Drunk Driving. Detroit: Greenhaven Press, 2007.