Field Sobriety Testing

When a driver of a vehicle is stopped by the police in Las Vegas under suspicion of drunk driving (also known as “Driving under the Influence or “DUI”) the police officer who pulled you over will usually require that you undergo a series of tests known as “Field Sobriety Tests.”

In the past, police officers would often do their own unmonitored testing to try and assess whether a driver was impaired or “under the influence.” This would include random and oftentimes silly tests such as counting backwards, reciting the alphabet between certain letters, or touching one’s nose with their own finger. Eventually however, the National Highway Traffic Safety Administration (“NHTSA”) collected information which, according to that organization, most accurately evaluates a person’s impairment and thus, their ability to drive.

Do They Work?

Many people just assume that because police conduct these tests, they must be accurate. The unfortunate truth is that they often are not.

To better understand the field sobriety tests and the thought process of the NHTSA behind them, you can read the NHTSA Appendix.

As outlined below, there are literally hundreds of ways the tests can be improperly evaluated or administered that can lead to inaccurate results.

What are the Standard Field Sobriety Tests?

Historically, there were literally dozens of different types of methods concocted by police officers in order to attempt to evaluate the level a person’s impairment and determine if they are under the influence. Based on the reasons outlined elsewhere on this page, these have, for the most part, been restricted by law enforcement (and specifically law enforcement in Las Vegas and throughout Nevada) to three (3) different tests, called "field sobriety tests." The most commonly used tests are the “walk-and-turn,” the “one-leg-stand,” and the “HGN” or “horizontal gaze nystagmus” test. Each is explained further below:

Horizontal Gaze Nystagmus (“HGN”)

The Horizontal Gaze Nystagmus evaluates the phenomenon where a person’s eye involuntary jerks as the eye moves side to side. Normally, this nystagmus occurs when a person’s eye rotates at high peripheral angles. When a person has consumed alcohol to the point of impairment however, this so called nystagmus is more extreme and often occurs at lesser angles.

A person who is under the influence of alcohol often will have some problem with smoothly tracking a moving object with their eyes. During a properly administered HGN test, the law enforcement officer watches the path of a person’s eyes they visually follow a slowly moving object, usually a pen or small flashlight.

During this moving process, the examiner looks for three (3) indicators of impairment in each of the person’s eyes. Namely, the officer looks for the lack of the ability to follow the item smoothly, if “jerking” or “twitching” of the eye is distinctly recognizable when the eye is at maximum deviation and if whether the angle of the eye is 45 degrees of center at the onset of jerkin.

According to the NHTSA, if the two eyes combined show four (4) or more of these “clues” it is believed that the person driving is likely impaired by alcohol.

Walk and Turn

The Walk-and-Turn test requires the person taking it to listen to and follow instructions given by an officer while performing simple (for most healthy people under the right conditions) physical movements. The thought is that an impaired person may have difficulty performing tasks which require their attention to be split between mental and physical activities.

The Walk-and-Turn test requires the subject to listen to the instructions and then follow the directions - - to take nine steps, each heel-to-toe, along a perfectly straight line. At the conclusion of those nine (9) steps, the person is instructed to turn around on one foot and return along the same path in the same manner, but in the opposite direction.

The law enforcement officer giving the tests observes for signs of impairment, such as: the suspect not being able to maintain balance while listening to the officers instructions, the person beginning the physical portion of the exercise before the verbal instructions are finished, the person stopping while walking in order to regain balance, the persons heels and toes not touching during the steps, whether the person steps offline, whether a person uses their arms to balance, making an improper turn, or taking an incorrect number (either too many or too little) of steps.

One Leg Stand

In the One-Leg Stand test, the person suspected of being impaired is told to stand with one foot approximately six inches off the ground and count seconds aloud using the “thousands” between each number (…“one thousand-one, one thousand-two, one-thousand-three”… ) until they are told by the officer to put their foot down.

The police officer the “times” the subject for 30 seconds looking for four (4) separate and distinct factors, or indicators, of impairment. These include swaying while balancing, utilizing arms to maintain balance, hopping on one foot to balance, and putting the other foot down.

How Were the Tests Created?

Approximately 40 years ago, the Government, through the National Highway Transportation Safety Administration (commonly referred to as “NHTSA”) commissioned a group called the Southern California Research Institute (or “SCRI”) to study the many variations of testing done by law enforcement throughout the country in order to determine which tests best assessed impairment of drivers.

Unilaterally, the SCRI narrowed the tests down, from the literally dozens being used by police, to the six tests it thought best. The group then selected a tiny sample of police officers, ten in total, to observe hundreds of people who were provided with varying amounts of alcohol. This was what is called a “double-blind study” meaning that the people consuming alcohol and the police didn’t know how much they had been given to drink.

Officers were then asked to determine ONLY ONE THING - - namely, whether they believed the drinker had a blood-alcohol concentration (or “BAC”) which was higher than .10%.

After assessing the results of the ACTUAL BAC’s from the test subjects against the guesses of the police officers, the NHTSA began to universally recommend that law enforcement officers use only three (3) tests, which have not become STANDARDIZED FIELD SOBRIETY TESTS. They are: Horizontal Gaze Nystagmus (HGN), Walk and Turn, and One-Leg Stand.

The amazing thing that came from the test however, is not the fact that the NHTSA centralized testing to three (3) tests; it is that the NHTSA admitted and documented a rate of error among the police officers assessment of nearly half (47%). To put it in perspective, the officer’s trained assessment was actually no more likely to be correct than the odds of success spinning a Las Vegas roulette wheel.

Naturally, the extremely large rate of error led to the NHTSA commissioning yet another test, again conducted by Southern California Research Institute (or “SCRI”) to do a subsequent study in 1981.

In the second study, the stated goal of the NHTSA was to standardize the procedures used by law enforcement while administering the tests with the hope of lessening the egregious error rate revealed in the previous study.

The second study showed, according to the NHTSA, the following results: the HGN test, when given by itself, was accurate at detecting a BAC over .10 percent approximately 77% of the time; the Walk-and-Turn test was accurate 68% of the time and the One-Leg Stand was correct in approximately 65% of the tests. However, by its own admission, the NHTSA claimed, even given uniform standards for testing, that Police Officers were incorrect 18% of the time. A similar test was commissioned in 1983, which revealed similar results.

Since these commissioned studies were conducted by the NHTSA, numerous other studies have been conducted by scientists and universities from all over the United States which have revealed many issues and problems with the testing.

The Horizontal Gaze Nystagmus

One of the commonly identified problems with the HGN test is that it is subjective and only observable by the officer reporting the results. It stands to reason that a person accused of driving under the influence cannot see his or her own eyes. Likewise, in jurisdictions which videotape the tests (the Las Vegas Metropolitan Police Department does not equip their officers or patrol vehicles with video cameras, the Nevada Highway Patrol does) show the testing either. As such, neither a criminal Defendant, a Judge nor a Jury can review the results. Therefore, one is left with a situation where you have to take a police officer’s word as to whether the test was properly administered and what the results were. It us been shown in numerous studies that many officers incorrectly perform the tests and interpret the results. In fact, at least one study showed that law enforcement performs the test incorrectly 95 percent of the time.

Among the many numbers of mistakes that law enforcement can make when performing the HGN test are an incorrect number of passes, failure to follow the correct timing protocols for each pass and the failure to properly estimate a correct 45 degree angle. In addition, there are at least 35 other documented causes of nystagmus, including the most common, mere drowsiness.

The Walk and Turn

The instructions for the administration of the walk and turn test are contained in the policy manuals of the NHTSA. The 2002 edition of the manual dictates that the walk and turn test be split into two phases, namely “the instruction phase” and “the walking phase.”

In the instruction phase, the law enforcement officer requires the test taker to place his or her left foot on the line and likewise to place their right foot on the line in front of the left foot, all while the police officer provides the comprehensive instructions and then asks the subject if he or she understood them.

The officer then must then demonstrate the test, but the officer is only required to take a few steps (not the whole 9) and the turn. The officer then should tell the person taking the test to proceed with nine heel-to-toe steps, keeping their eyes on their feet and verbally counting each step out loud and to take then take nine heel-to-toe steps back to the starting point. The officer should also instruct the person that ‘once they start walking to not stop until the entire test is completed.

There are eight ‘‘clues’ of impairment which are associated with the walk and turn test. If the police officer observes two (2) clues out of the eight (8), the subject has “failed” the test.

As with the HGN test, there are a number of common mistakes made by officers when administering this test. Perhaps the most common is that the officer fails to identify a straight line for the test taker to walk. The NHTSA guidelines dictate that this needs to be done. In fact, the NHTSA specifically states that the ‘‘walk-and-turn test requires a designated straight line.’’ Among other problems with the test is that police officers often fail to take into consideration that every person is different. Many people struggle with balance, sober or not. While this fact is stated in the NHTSA manual, many times it isn’t accounted for by officers in the field. In addition, the NHTSA manual also states ‘… original research indicated that individuals over 65 years of age” or individuals with “back, leg or middle ear problems” have difficulty performing the test. The NHTSA has also identified wind and weather conditions, age, weight, and footwear as items that ‘‘may interfere with the suspect’s performance.’’

The One-Leg Stand

The remaining standardized Field Sobriety Test is the one-leg stand test. This rest requires the officer to instruct the subject to raise one leg approximately six inches above the ground, keeping the leg straight with the persons toes pointed forward and to count out loud for thirty (30) seconds using the ‘‘one thousand -one, one thousand – two, one thousand - three’ method’ until told to stop by the law enforcement officer. There are four (4) identified “clues” affiliated with the One Leg Stand test. Namely, thy are, if the subject uses arms for balance, sways, puts foot down or hops. If two (2) or more clues are observed by the officer, the subject will be considered to have “failed” the test.

Among the many problems with the test is that it is not scored properly, meaning that the officer often includes observations above and beyond the standardized clues. Another problem is that the test is invalid when the officer does not provide a dry, hard, level, and non-slippery surface. As with the walk and turn test, the NHTSA manual acknowledges that ‘…research indicates that certain individuals over 65 years of age” and those with “back, leg or middle ear problems, or people who are overweight by 50 or more pounds had difficulty performing this test.” The test also dictates that individuals taking the test with heels more than two inches high should be given the opportunity to remove their shoes as this can skew the test.

Are the Field Sobriety Tests Required

Many drivers assume that because a police officer asks you to perform these tests, that you must perform them. This isn’t the case. Field Sobriety Tests are OPTIONAL. (In some cases however, there are consequences for refusing to do field sobriety tests. Police often interpret the refusal to perform field sobriety tests as being indicative of “probable cause” of driving under the influence and require that the driver submit to full evidentiary testing, such as a blood test).

driver is perfectly within his or her rights to refuse to take any field sobriety tests. While they have long been held out as indicative of a driver’s “impairment” field sobriety tests do not actually measure impairment, and are not actually tests. In reality, they are specifically designed physical agility exercises, are evaluated under extremely subjective standards and are designed so that the person being tested will fail. A person who has had nothing to drink or someone that has only had a drink or two and is under the legal limit, often will “fail” these tests. Nevertheless, in Nevada, a “failure” at these difficult and subjective tests is enough probable cause to someone to be arrested and taken to jail.

Contact Us Today

If you have been arrested for a DUI, or know someone who has, we can help. If you want to ask us questions about your rights, discuss the legality of the field sobriety tests administered to you, or request a FREE COPY of your Nevada Driver’s Rights Card, call us today at (702) 895-6760 or submit your case online today. We offer a FREE, no obligation case evaluation with our experienced DUI attorney. Just because you were arrested, DOES NOT mean you must be convicted! Contact the law firm of Hofland & Tomsheck “Fighting for Justice, Fighting for YOU!”

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