Texas DWI Indicators and Sobriety Tests

Types of DWI Field Sobriety Tests and How They Work

Driving while under the influence of alcohol or narcotics is extremely dangerous. Every year, it causes a large number of traffic fatalities. Unfortunately, many Americans continue to choose to drive while under the influence of various substances. They believe they can still make good decisions, despite the fact that this is not the case. Those who drive while intoxicated have slower reaction times and make poor decisions. They endanger themselves as well as others.

Law enforcement officers have the authority to stop any vehicle they suspect of being intoxicated while driving. Breath testing with a breathalyzer is frequently used to determine sobriety. If the police officers suspect the driver of drunk driving, the test will look at the driver’s blood alcohol content (BAC).

Only the presence of alcohol can be detected by a breath test. It examines only blood alcohol levels and nothing else. It is unable to determine whether or not the driver is under the influence of drugs. Most officers will administer a field sobriety test in these circumstances. Three different sobriety tests are commonly used to determine whether an individual is driving while intoxicated (DWI).

Standardized Field Sobriety Test

Standard Field Sobriety Tests (SFST) are usually administered when a police officer has a reasonable articulable suspicion that a driver has broken Texas DWI law. An officer can use the failure of one or more of the SFSTs to establish probable cause to make a valid DWI arrest.

The Standardized Field Sobriety Test (SFST) is a battery of three tests that are administered and evaluated in a consistent manner in order to obtain validated indicators of impairment and establish probable cause for arrest. These tests were created as a result of research conducted by the Southern California Research Institute and funded by the National Highway Traffic Safety Administration (NHTSA). A formal training program was developed and is available through NHTSA to assist law enforcement officers in becoming more skilled at detecting DWI suspects, describing their behavior, and providing effective testimony in court. The International Association of Chiefs of Police is in charge of the program’s formal administration and accreditation (IACP). The SFST consists of three tests:

HGN Exam

Horizontal Look Nystagmus is an involuntary jerking of the eye that occurs when looking to the side. Nystagmus occurs when the eyes are rotated at high peripheral angles under normal conditions. However, when a person is under the influence of alcohol, nystagmus is exaggerated and may occur at smaller angles. An alcoholic will frequently have difficulty smoothly tracking a moving object. The officer observes a suspect’s eyes as the suspect follows a slowly moving object, such as a pen or small flashlight, horizontally with his or her eyes in the HGN test. The examiner looks for three signs of impairment in each eye: if the eye cannot smoothly follow a moving object, if jerking is noticeable when the eye is at maximum deviation, and if the angle of onset of jerking is within 45 degrees of center. If four or more clues appear between the two eyes, the suspect most likely has a BAC of 0.08 or higher. According to NHTSA research, this test correctly classifies approximately 88 percent of suspects (Stuster and Burns, 1998). HGN may also be associated with the use of seizure medications, phencyclidine, a variety of inhalants, barbiturates, and other depressants.

Walk and Turn Test

The Walk-and-Turn test and One-Leg Stand test are “divided attention” tests that most unimpaired people can perform. They demand that the suspect listen to and follow instructions while performing simple physical movements. Impaired people struggle with tasks that require them to divide their attention between simple mental and physical exercises.

The Walk-and-Turn test instructs the subject to take nine heel-to-toe steps along a straight line. Following the steps, the suspect must turn on one foot and return in the opposite direction. The examiner looks for eight indicators of impairment: if the suspect cannot keep balance while listening to the instructions, starts before the instructions are finished, stops while walking to regain balance, does not touch heel-to-toe, steps off the line, uses arms to balance, makes an incorrect turn, or takes the wrong number of steps. According to NHTSA research, 79 percent of people who exhibit two or more indicators during the test will have a BAC of 0.08 or higher.

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 in the One-Leg Stand test. The officer counts down 30 seconds for the subject. Swaying while balancing, using arms to balance, hopping to maintain balance, and putting the foot down are all indicators of impairment. According to NHTSA research, 83 percent of people who exhibit two or more of these indicators during the test will have a BAC of 0.08 or higher.

Intoxilyzer 5000

The Intox 5000’s basic operation is infrared spectroscopy combined with computer programming that converts a measurement in reduced light to units of alcohol measurement (gm / 210 liters). The machine accomplishes this by measuring the energy of infrared light in the sample chamber. The light we see is only a small part of a much larger spectrum of electromagnetic radiation. This “machine” can see the entire spectrum as it relates to certain compounds that may be linked to alcohol consumption.

  • When a subject’s breath enters the sample chamber, the photodetector detects any decrease in light emitted by the light bulb. The amount of reduction is then entered into a computer program that converts the reduced light into grams of alcohol, which is then expressed as grams per 210 liters of air. Much remains unknown about how the computer performs this critical calculation at this time, as CMI claims it is a “trade secret” that cannot be shared with the public or even law enforcement. To summarize, anything that the Intox 5000 misidentifies as an ethanol molecule will affect the results.

Within the sample chamber, the Intox 5000 does not actually measure grams of alcohol. It measures the amount of light energy absorbed by the bonds that connect the atoms in the ethanol molecule. Molecules are not rigid, static objects. The bonds that connect the atoms act more like springs than rods, bending and stretching while holding the atoms within the molecule together.

Some of the factors that can influence a breathalyzer reading and cause it to produce an incorrect result are as follows:

  • Chemical exposure to (1) xylenes (2) acetone (3) toluene (4) acetaldehyde (5) isopropyl alcohol (6) methanol
  • Airbag deployment – the dust emitted by airbag deployment can cause the Intox 5000 to measure less light.
  • Isopropyl alcohol is actually released from the body as a result of the Atkins Diet.
  • Gastroesophageal Reflux Disorder – If a subject has reflux symptoms just before or during testing, the machine will read all alcohol in the sample and assume that it is all from the lungs.

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