"Field Sobriety Tests" in Las Vegas, NV DUI cases

Field sobriety tests ("FST's") 
are exercises Nevada police ask DUI suspects to perform to help determine whether the suspects are intoxicated. The three standardized FSTs are:

  1. Horizontal gaze nystagmus (the penlight test)
  2. Walk and turn
  3. One-legged stand

The federal agency NHTSA (National Highway Traffic Safety Administration) developed these FSTs and provide police officers with detailed instructions on how to administer and score them. But in practice, FSTs are not always reliable indicators of impairment.

Poor FST performance can result from factors unrelated to drug or alcohol use, such as:

  • improper administration of the tests by police,
  • unfavorable settings and surroundings,
  • certain medications, and
  • illness or injury

A skilled Nevada criminal defense attorney may be able to show that a failing FST score is inaccurate and that any DUI charges should be dropped.

In this article, our Las Vegas Nevada DUI attorneys discuss:

field sobriety tests: W&T
Nevada police ask DUI suspects to perform three field sobriety tests including the "walk-and-turn" test.

1. What are standardized field sobriety tests in Nevada DUI cases?

Standardized Field sobriety tests (FST's) are physical exercises that police ask DUI suspects to perform in an effort to determine whether the suspects are indeed under the influence of drugs or alcohol. Through NHTSA, the US Department of Transportation outlines specific instructions about how to administer the tests, and what "clues" police should look for to detect intoxication.

After a police officer pulls over DUI suspects, first the officer will ask the suspects some cognition-testing questions such as requesting that they take out their driver's license and registration. Meanwhile, the officer will closely observe the suspects' demeanor for signs of intoxication, including:

  • the odor of alcohol or marijuana
  • glassy, watery, or red/bloodshot eyes
  • flushed face
  • lack of coordination
  • slurred speech or slow responses
  • open containers or drug paraphernalia in the vehicle

When suspects are manifesting such signs of intoxication, the police officer will then ask them to exit the vehicle and perform the FSTs. Nevada's standardized FSTs consist of three separates tests:

  1. Horizontal Gaze Nystagmus,
  2. Walk-and-Turn, and
  3. One-Legged-Stand1

The D.A. may use the results of these FSTs in court to try to prove that the suspect was impaired while driving.

1.1. Horizontal Gaze Nystagmus (HGN)

Also called the pen test, the Horizontal Gaze Nystagmus test is an eye-test where the suspect is instructed to keep his/her eyes fixed on the officer's penlight (or another object) as the officer moves it from side to side. In the meantime, the officer is observing the suspect's pupils for an involuntary jerking -- called "nystagmus" -- which can be a sign of intoxication.

Specifically, the police officer is checking for three "clues" of intoxication in each eye:

  1. Lack of smooth pursuit. This is where the pupil spontaneously jerks while following the police officer's penlight. Theoretically, a sober person's eyes would move smoothly.
  2. Distinct nystagmus at maximum deviation. For four (4) seconds, the officer holds the penlight very far to the side so the suspect's pupils are at "maximum deviation." If the pupils bounce, it may be a sign of intoxication.
  3. Onset prior to 45 degrees. As the officer moves the penlight back and forth, the officer is studying whether the suspect's pupils jerk prior to the penlight being at a 45-degree angle away from the suspect's face. If the pupils do jerk, it could be a sign of intoxication.

During the HGN, the officer is tallying how many "clues" each eye is exhibiting. The maximum number of clues a suspect can show is six (6) (which is three (3) for each eye). Exhibiting four (4) or more clues is a failing score.2

1.2. Walk-and-Turn (WAT)

The Walk and Turn test is a physical agility and coordination test. The suspect is instructed to take nine (9) steps heel-to-toe back and forth. In addition, the suspect has to keep one foot on the ground as he/she pivots around during the halfway point. Finally, the suspect has to count the numbers aloud.

In the meantime, the police officer is looking for eight "clues" of intoxication:

  1. The suspect cannot keep balanced while the police officer is giving him/her instructions.
  2. The suspect starts to walk before the police officer finishes giving the instructions.
  3. The suspect pauses during the walk to steady him/herself. (Note that walking slowly is okay as long as there is no stopping.)
  4. The suspect is not walking heel-to-toe.
  5. The suspect steps out of line.
  6. The suspect uses his/her arms to balance.
  7. The suspect loses his/her balance while doing the turn.
  8. The suspect takes more or less than the nine steps required in each direction.

Showing two (2) or more clues during the WAT test is a considered failing score.3

1.3. One-legged stand (OLS)

For the One Leg Stand test, Nevada police have the suspect stand in place on one leg while keeping the other leg extended forward about six (6) inches off the ground. Simultaneously, the suspect has to count aloud to 30 by reciting "One one-thousand, two one-thousand, three one-thousand..." etc.

Like the WAT, the OLS is considered a "divided attention" test because the suspect's mind has to multi-task between a physical exercise and counting aloud.

Meanwhile, the police officer is looking out for the following four "clues" of intoxication:

  1. The suspect hops.
  2. The suspect puts a foot down.
  3. The suspect uses arms for balance.
  4. The suspect sways while balancing.

Exhibiting two (2) or more clues in the OLS test is deemed a failing score. Incorrectly counting the numbers does not negatively impact the score.4

1.4. After the field sobriety tests

When a DUI suspect does not pass the FSTs, police officers will then ask the suspect to submit to a preliminary breath test (PBT). Then depending on the results and surrounding circumstances, the officers may believe they have probable cause to arrest the suspect for DUI.5

DUI suspects who pass the field sobriety tests are usually released at the scene. Depending on the reason they were pulled over, the officer may issue them a traffic citation such as speeding.

Note that whether a suspect gets arrested for DUI is up to the police officer's discretion. In some cases, the police may decide there is probable cause to believe drivers are under the influence even if they pass the FSTs and PBT.

1.4.1. Evidentiary tests

Once DUI suspects are arrested and booked, they are required to submit to an evidentiary DUI breath test or a DUI blood test. Note that suspects accused of DUI of controlled substances have to take the blood test since breath tests do not register narcotics levels.6

Defendants who refuse to submit to an evidentiary breath or blood test can be physically constrained in order to give a blood sample. The police officer just needs to get a court order first in order for the blood test results to be admissible in court.7

2. Am I legally required to take field sobriety tests in Las Vegas, Nevada?

No. FSTs are not mandatory even though the police may say that they are.8

Some suspects politely elect to decline the FSTs since even sober people have a substantial likelihood of failing them. And by not taking the test, the state has less evidence to prove its case against the suspect.

However, declining the FSTs will likely ensure that the police officer will arrest the suspect for DUI. In practice, police usually construe refusals to perform FSTs as a "consciousness of guilt."

Note that officers will not administer FSTs tests on DUI suspects who are clearly too incapacitated or injured to comply.9 Officers should also not administer FSTs if there is not a safe and appropriate space on which to perform them.10

3. Are FSTs scientifically valid?

This is an issue of debate. NHTSA claims that correctly administered FSTs are sufficiently reliable to determine whether a driver is under the influence. But statistically, one out of four people who fail FST's is not under the influence of drugs or alcohol. And the tests' accuracy rates are very low:11

Standardized Field Sobriety Test Reliability Rate for Determining DUI

Horizontal Gaze Nystagmus


Walk and Turn


One-legged Stand


"False positives" from FSTs can be caused by various circumstances such as:

  • Poor testing conditions:
    • road and sidewalk surfaces that are uneven, soft, wet, or slippery
    • windy or rainy weather
    • unsuitable footwear, or lack of footwear
    • poor lighting for the officer to observe the suspect
    • disruptive visual and audial distractions such as traffic, bright lights, sirens, honking, and spectators
  • Adverse physical or medical conditions:
    • fatigue
    • anxiety
    • inner ear problems
    • mental disabilities
    • prescribed medication that may hinder coordination or cause nystagmus
    • physical limitations such as old age, injury, illness, or obesity
    • tight or uncomfortable clothing
  • Officer misconduct:
    • intimidation
    • incorrect, inaudible, or misleading instructions and directions
    • distracting movements or statements
    • bias against the suspect

In sum, there are several factors that can cause a sober person to exhibit false clues during FST's in Nevada.

3.1. Non-standardized Field Sobriety Tests

finger to nose

NHTSA considers the HGN, WAT and OLS tests to be "standardized" field sobriety tests. This is because...according to NHTSA...studies show some correlation between the test results and the driver's impairment.

Some "non-standardized" field sobriety tests exist, but Nevada police rarely use them. This is because no national, reliable studies exist that demonstrate any correlation between the test results and the driver's impairment. These non-standardized FSTs are:

Non-standardized FSTs Instructions

Rhomberg stationary balance test

The suspects stand upright with feet together while leaning their head back and holding out their arms to the side.

Finger-to-nose test

The suspects close their eyes, reach out their dominant arm, and then try to touch their nose with their index finger. This is a routine test in neurology exams.

Finger count test

The officer raises his/her hand, and the suspects count the number of fingers the officer is displaying. This test is meant to detect whether the suspects' vision is blurry.

Hand pat test

Suspects extend one arm in front of them palm up. Then they place their other hand on top of the first palm down. Then the top hand pats the bottom hand while flipping it 180 degrees between pats. Meanwhile, the suspects count aloud, "one, two, one, two..." in relation to every pat.

Vertical gaze nystagmus

The officer holds up a penlight about a foot in front of the suspects' nose and moves it up and down. Then the suspects keep their head still while following the stimulus with their eyes.

ABC test

The officer asks suspects to recite a portion of the alphabet.

Numbers backward test

The officer asks suspects to count backward from one number to another.12

When a Nevada police officer does administer these non-standardized FSTs, the DUI defense attorney can seek to have them excluded from evidence for lack of scientific basis.

4. How does an attorney attack the FSTs in a Nevada court?

Common defenses to invalidate FST include showing the court that:

  1. The FSTs are unreliable
  2. The setting was improper
  3. The suspect's physical conditions caused a false positive
  4. The police made mistakes

4.1. The FSTs are unreliable

As discussed in the previous section, FSTs have a significant fail rate. 25% of people who fail FSTs are in fact sober. And depending on the test, the FSTs are only 65% to 77% reliable.

Furthermore, FSTs are their least unreliable when the suspect is perfectly healthy, physically fit, wide awake, mentally uncompromised, emotionally calm, and wearing athletic clothing. Most DUI suspects fall short of these standards. Any reasonable person would be extremely nervous to perform FSTs and would find the FST instructions very confusing. 

A defense attorney would argue that these statistics and common-sense facts should cast significant doubt on the defendant's FST results. 

4.2. The setting was improper

FSTs must take place in an environment that maximizes the suspect's chances of success. As discussed in the previous section, FSTs can render false positives by a

  • poor walking surface,
  • inclement weather,
  • disruptive noises, and
  • other variables.

A DUI defense attorney should conduct a thorough investigation to find video surveillance footage and eyewitness testimony. Such evidence may be able to show that the surrounding circumstances set up the defendant to fail the FSTs.

4.3. The suspect's physical condition caused a false positive

As discussed in the previous section, several medical and psychological conditions can prohibit a sober person from passing FST tests. For example, a head injury may cause nystagmus13; a bad back could make it impossible to perform the one-legged stand; high anxiety could keep a suspect from remembering all the instructions for the walk-and-turn.

A defense attorney could use the defendant's medical records to help show that he/she was physically unable to pass the FSTs.

4.4. The police made mistakes

Scoring FSTs is extremely subjective. Maybe the officer thought he/she saw the suspect exhibit a "clue" when in fact it was too dark out to see clearly. Or perhaps the police forgot to mention that arms cannot be used for balance during the WAT and OLS, and the suspect used his/her arms without realizing it was against the rules.

The police officer's body cam or dash cam footage could prove invaluable in showing that the police officer was at fault for the suspect's failing FST scores.

In addition, the defense attorneys should aggressively cross-examine the officers during the Nevada DMV hearing. (The DMV Hearing is like a mini-trial where DUI defendants can contest the DMV's revocation of their driver's license.) Since the DMV case is separate from the criminal case, the DMV hearing is a good opportunity to test the officer's credulity and uncover weak spots in the state's evidence that can then be used in the defendants' favor in the criminal case.

When an attorney uncovers problems with the FSTs, it gives her a bargaining chip when negotiating with the prosecutor. Perhaps the D.A. would be willing to reduce the Nevada DUI charges to reckless driving or even a full dismissal. And if the case goes to trial, such evidence may make it impossible for the prosecutor to prove guilt beyond a reasonable doubt.

Arrested for DUI? Call a lawyer...

702-DEFENSE (702-333-3673)
Call our Las Vegas drunk driving attorneys at 702-DEFENSE for a FREE consultation.

If you have been accused of driving while impaired, call our Las Vegas criminal defense attorneys at 702-DEFENSE (702-333-3673) for a free consultation. We will investigate every aspect of your case including the FSTs to try to get the charges reduced or dismissed. And if necessary, we can take the matter all the way to trial in pursuit of a not guilty verdict.

We represent clients throughout Nevada, including Las Vegas, Henderson, Washoe County, Reno, Carson City, Laughlin, Mesquite, Moapa, Elko, Pahrump, and Tonopah.

Arrested in California? See our article on field sobriety tests in California DUI law.

Arrested in Colorado? See our article on field sobriety tests in Colorado DUI law.

Legal References:

  1. U.S. Department of Transportation "DWI Detection and Standardized Field Sobriety Testing" NHTSA Student Manual (October 2015).
  2. Wilkinson, Kime (1974) (oral dose of alcohol-impaired eye movement of all subjects); Lehti, The Effect of  Blood Alcohol Concentration on the Onset of Nystagmus, 136 BLUTALKOHOL 414 (West Germany 1976); NHTSA Student Manual (2006) at VIII/4.
  3. NHTSA Student Manual at VIII/4.
  4. Id., at VIII/13, VIII/14, and VII/6.
  5. NRS 484C.150. Note that DUI suspects give "implied consent" to take a PBT. Suspects who refuse will have their license confiscated immediately and face a one (1) year-long license revocation.
  6. NRS 484C.160. Note that DUI suspects give "implied consent" to take an evidentiary breath or blood test; Missouri v. McNeely, 569 U.S. 141, 133 S.Ct. 1552 (2013).
  7. NHTSA Student Manual at VIII/7.
  8. See e.g.Department of Motor Vehicles & Pub. Safety v. Evans, 952 P.2d 958, 114 Nev. 41 (1998) (the defendant refused to take two of the three FSTs).
  9. See e.g.Department of Motor Vehicles v. Torres, 779 P.2d 959, 105 Nev. 558 (1989) (the defendant was asleep behind the wheel).
  10. See e.g., Department of Motor Vehicles & Pub. Safety v. Becksted, 813 P.2d 995,107 Nev. 456 (1991) ("No field sobriety test was administered for safety reasons.")
  11. NHTSA Student Manual at VIII/3-14; see also Stuster &Burns, Validation of the Standardized Field Sobriety Test Battery at BACs Below .10 percent, U.S. Dept. of Transportation Rep. No. Dot-HS-808-839 (1998), at 33; Burns & Moskowitz, Psychophysical Tests for DWI Arrest, U.S. Dept. of Transportation Rep. No. DOT-HS-802-424 (1977); Anderson, Schweitz & Snyder, Field Evaluation of Behavioral Test Battery for DWI, U.S. Dept. of Transportation Rep. No. DOT-HS-806-475 (1983).
  12. fieldsobrietytests.org.
  13. See e.g., Department of Motor Vehicles & Pub. Safety v. McLeod, 801 P.2d 1390, 106 Nev. 852 (1990) (field sobriety tests were invalidated because of defendant's head injury).

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