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Standard Field Sobriety Test

The Standardized Field Sobriety Test (SFST) battery is composed of three tests:

  1. Horizontal Gaze Nystagmus (HGN)
  2. Walk-and-Turn (WAT)
  3. One-Leg Stand (OLS).

The tests were developed by the National Highway Traffic Safety Administration (NHTSA) in the late 1970’s. In 1981, law enforcement officers began using NHTSA’s Standardized Field Sobriety Test (SFST) battery at roadside to help determine whether motorists who are suspected of DWI have blood alcohol concentrations (BAC’s) greater than 0.10 percent. Since 1981, however, many states including Texas have implemented laws that define DWI at BAC’s below 0.10.

The validity of SFST results is dependent upon officers following the established, standardized procedures for test administration and scoring. According to NHTSA when properly administered and scored, under laboratory conditions, the accuracy of the SFSTs in correctly identifying intoxicated drivers is as follows:

  • HGN – 77%
  • WAT – 68%
  • OLS – 65%

This means that even under laboratory conditions, the HGN was wrong 23% of the time, the WAT 32% and the OLS 35% of the time. Additionally, NHTSA’s own research emphasizes that test results are valid only when administered in strict compliance with NHTSA protocol. If anyone of the standardized field sobriety elements is changed, the validity is compromised. It is therefore imperative to have your attorney review the manner in which the SFST’s was administered. Your lawyer may be able to suppress the results of an improperly administered test.

HGN – Horizontal Gaze Nystagmus

“Nystagmus” means an involuntary jerking of the eyes. HGN refers to an involuntary jerking occurring as the eyes gaze toward the side. In addition to being involuntary the person experiencing the nystagmus is unaware that the jerking is happening. The theory behind the test is that nystagmus becomes readily noticeable when a person is impaired.

In administering the test the officer has the subject follow the motion of a stimulus with the eyes only. The stimulus may be the tip of a pen or penlight, an eraser on a pencil or a fingertip. As the eyes move from side to side each eye is examined for three specific clues:

  • Lack of Smooth Pursuit – does the eye move slowly or does it jerk noticeably?
  • Distinct Nystagmus at Maximum Deviation – when the eye moves as far to the side as possible and is kept at that position for several seconds, does it jerk distinctly?
  • Onset of Nystagmus Prior to 45% – as the eye moves to the side, does it start to jerk prior to a 45% angle?

Officers frequently fail to properly administer the HGN. It is crucially important for your attorney to review the videotape, if available to ascertain whether the test was properly administered or whether suppression of the results is possible.

Walk and Turn

The WAT is a divided attention test consisting of two stages: Instruction Stage; and Walking Stage. In the instruction stage, the subject must stand with their feet in heel-to-toe position, keep their arms at their sides, and listen to instructions. The subject must maintain the heel-to-toe position and may not begin walking until all instructions are given. In the Walking Stage the subject takes nine heel-to-toe steps, turns in a prescribed manner, and takes nine heel-to-toe steps back, while counting out loud and watching their feet. Officers observe the subject’s performance for eight clues:

  • can’t balance during instructions
  • starts too soon
  • stops while walking
  • doesn’t touch heel to toe
  • steps off line
  • uses arms for balance
  • loses balance on turn or turns incorrectly; and
  • takes the wrong number of steps

A subject who exhibits two or more clues will fail the test. Scoring is entirely subjective and within the officer’s discretion.

One Legged Stand

The OLS is also divided into two stages. In the Instruction Stage, the subject must stand with feet together, keep arms at side and listen to instructions. In the Balance and Counting Stage, the subject must raise the leg of his choice approximately 6 inches off the ground, toes pointed out, keeping legs straight. While looking at the elevated foot, count out load in the following manner: “one thousand and one”, “one thousand and two”, etc, until told to stop. The officer will instruct the subject to stop after 30 seconds. The subject is observed for the following clues:

  • sways while balancing
  • uses arms to balance
  • hops
  • puts foot down

A subject who exhibits 2 or more clues, as determined by the officer, will fail the test.


Person is instructed to stand with feet together, head tipped back, eyes closed, arms at side. Position is demonstrated. Observe anterior-posterior sway, 30 sec. trial. This is not one of the “Standardized” Field Sobriety Tests. Typically estimating 30 seconds within 5 seconds either way is considered good, anything outside of a 5 second margin of error will be counted as a sign of intoxication. The officer will also look for swaying during this time.

Breath Test – Chemical Test

Under Texas law an individual is legally intoxicated if his/her alcohol concentration is .08 or greater. A person’s alcohol concentration can be determined by testing the blood, urine or breath. “Alcohol concentration” means the number of grams of alcohol per:

  • 210 liters of breath;
  • 100 milliliters of blood; or
  • 67 milliliters of urine.

Blood testing is generally considered to be the most reliable and accurate, while urine tests are regarded as the least precise. If you are arrested in the state of Texas you will most likely be asked to give a sample of your breath. Breath testing is the most commonly utilized method because it is the least expensive to administer and in most cases, more convenient as well. The scientific community is sharply divided over the accuracy and reliability of breath testing procedures. The police do not save the sample of breath tested. Thus it is not available for re-testing by an independent laboratory.