Field Sobriety Tests in Colorado DUI Cases

In Colorado, standardized field sobriety tests (SFSTs) are a tool that police use during a DUI traffic stop to determine whether you are under the influence of alcohol and/or drugs. The exercises are optional, meaning you can refuse to take them without penalty.

We recommend that you politely refuse to take the SFSTs since they are more likely to hurt than to help your case in court.

In Colorado, officers use three standardized field sobriety tests (also called “voluntary roadside maneuvers”):

1. HGN – Horizontal Gaze Nystagmus (the eye test),
2. WAT – Walk and Turn, and
3. OLS – One Leg Stand.

These tests have been standardized by the National Highway Traffic Safety Administration (NHTSA) and are considered the most reliable of all the field sobriety tests. The results have been independently validated in a 1995 report by the Colorado Department of Transportation (CDOT).¹

Though even under ideal conditions, SFSTs often produce false positives and lead to false arrests for:

• DUI – driving under the influence of alcohol or drugs,
• DUI Per Se – driving with a BAC (blood alcohol concentration) of .08% or higher,
• DWAI – driving while ability impaired,
• Excess BAC CDL – driving a commercial vehicle with a BAC of .04% or higher, or
• UDD – underage drinking and driving (under-21 drivers with a BAC of .02% to .05%).

In this article, our Colorado DUI defense lawyers will address the following issues regarding standardized field sobriety tests (SFSTs):

• 1. Types of SFSTs
• 2. Accuracy
• 3. Your Rights
• 4. Fighting SFST Results
• 5. Other Tests
• Frequently Asked Questions
• Additional Reading

1. Types of SFSTs

Horizontal Gaze Nystagmus (HGN)

The first Colorado field sobriety test you will be asked to take is the horizontal gaze nystagmus (HGN) test.

Horizontal gaze nystagmus is an involuntary jerking motion that occurs when you move your eyes to the side. You cannot control horizontal gaze nystagmus if you have it, and you are unaware that it is happening.

To test you for horizontal gaze nystagmus, the officer will instruct you to stand with your feet together and your hands at your sides. You will then be told to hold your head still and follow the motion of a small stimulus with your eyes only – usually the tip of a pen or penlight. The officer will conduct two “passes” with each eye, beginning with your left eye.

The officer is looking to see if you exhibit any of these six “clues” that could indicate impairment by alcohol and/or drugs:

1. Your right eye is unable to track the stimulus smoothly,
2. Your left eye is unable to track the stimulus smoothly,
3. Your right eye exhibits sustained jerking when you look to the side,
4. Your left eye exhibits sustained jerking when you look to the side,
5. The onset of nystagmus occurs before your right eye has tracked 45 degrees, and/or
6. The onset of nystagmus occurs before your left eye has tracked 45 degrees.

Showing four or more “clues” is a failing HGN score.

Horizontal gaze nystagmus can be caused not only by drugs and/or alcohol. It can also be caused by medical and atmospheric conditions such as:

• Changes in barometric pressure,
• Extreme temperatures,
• Your biorhythms,
• Viral or bacterial infections,
• Inner ear conditions,
• Eye diseases,
• Albinism,
• Vitamin deficiencies,
• Glaucoma,
• Sunstroke,
• Neurologic disorders (such as multiple sclerosis or epilepsy),
• Endocrine conditions (such as thyroid disease or diabetes mellitus),
• Cardiovascular disease,
• Some prescription medications, and
• Innocuous substances such as caffeine, nicotine or aspirin.

In addition, fatigue and stress can make nystagmus worse.²

Walk and Turn (WAT)

Driving is a complex “divided attention” task. Drivers must simultaneously steer and accelerate or brake while at the same time reacting to a constantly changing environment.

Alcohol and drugs reduce the ability to divide attention between tasks. The “Walk and Turn (WAT) test” looks for your inability to do this by having you try to perform two tasks at once: Walking heel-to-toe and counting.

For the WAT, the officer will instruct you to stand with your feet in a heel-to-toe position and with your arms at your sides. You will then be asked to take nine heel-to-toe steps, turn in a prescribed manner, and take nine similar steps back, while counting the steps out loud. This tests your ability to divide your attention between listening, understanding and carrying out the instructions.

The Walk and Turn test is interpreted in a standardized manner – that is, the same way every time. The officer will look for eight “clues” that might indicate you are intoxicated:

1. You cannot keep your balance while listening to the instructions,
2. You start too soon,
3. You stop while walking,
4. You do not touch heel to toe,
5. You step off the line,
6. You use your arms for balance,
7. You make an improper turn, or
8. You take an incorrect number of steps.

Exhibiting two or more “clues” is a failing WAT score.

However, many factors other than alcohol and/or drugs can affect your ability to walk and turn as instructed. In particular, you might find the WAT test difficult even when sober if:

• You are overweight,
• You have mobility problems,
• You have difficulty balancing,
• You have problems with your feet, or
• You are ill or injured.³

One Leg Stand (OLS)

Like the Walk and Turn test, the One Leg Stand test (OLS) is a divided attention test.

The officer will instruct you to stand with your feet together and with your arms at your sides. You will then be told to raise one foot six inches off the ground while keeping both legs straight. You will be asked to look at your elevated foot and count “one thousand one,” “one thousand two,” “one thousand three,” etc., until told to stop 30 seconds later.

The OLS divides your attention between balancing on one foot and counting aloud. The accuracy of the test depends on it being given for at least 30 seconds. While many impaired people can stand on one leg for up to 25 seconds, few can do so for 30 seconds.

The officer is looking for four specific “clues” of intoxication during the One Leg Stand test:

1. You sway while balancing,
2. You use your arms to balance,
3. You hop, or
4. You put your foot down before the 30 seconds are up.

Exhibiting two or more “clues” is a failing OLS score.

As with the other SFSTs, the test may not be accurate if you have certain medical problems or issues with balance and/or mobility.⁴

2. Accuracy

NHTSA has claimed that the three standardized field sobriety tests can generally detect a blood alcohol concentration (BAC) of at least .10%. More recently, NHTSA has reported that the SFSTs can also detect a BAC of .08% (Colorado’s minimum limit for DUI per se) and even .04% (the minimum limit for drivers of commercial vehicles).

In reality, each SFST’s accuracy level for detecting an unlawful BAC is alarmingly low:

• HGN – 77%.
• WAT – 68%.
• OLS – 65%.⁵

Furthermore, the reported accuracy of SFSTs is based on tests in a controlled environment. The actual conditions under which you are given the tests – usually by the side of the road – are far from controlled.

Even NHTSA admits that accuracy levels of SFSTs can decrease based on certain factors in addition to those set forth above. These include (but are not limited to):

• The officer is not well-trained in detecting the signs of impairment,
• The impairment is caused in whole or in part by drugs and not alcohol,
• Inadequate lighting in the test area,
• Uneven ground,
• Your height restricts the officer’s ability to see your eyes clearly, or
• You are wearing clothing that makes the test difficult.⁶

3. Your Rights

During a Colorado traffic stop, you have to show the officer your driver’s license, registration, and insurance if asked. If you do not have an ID, you have to tell them your name and address if asked.⁷

You are under no obligation to answer any other questions or to take any field sobriety tests. (Plus, you have no obligation to take the preliminary breath test – a pre-arrest roadside breathalyzer test – unless you are under 21.)⁸

These tests are simply tools to help the officer decide whether there is probable cause to arrest you for DUI. You are under no obligation to incriminate yourself, and there are no consequences if you refuse to take the SFSTs.

If you do agree to take the SFSTs, however, the results can be used against you in court.⁹ That is why if an officer asks you to take SFSTs, it is generally best to politely decline them.

4. Fighting SFST Results

Our experienced Colorado DUI lawyers know that standardized field sobriety tests are at best just evidence of impairment – not proof. As discussed above, SFSTs are subject to a wide variety of errors and are frequently inaccurate, even under the best of circumstances.

We explain all this to the jury and offer alternative explanations for your SFST performance, such as:

• A medical condition,
• Prescription medication that did not affect your driving,
• Your weight,
• Mobility issues,
• Injury,
• Illness,
• Uneven ground,
• Poor visibility at the test site,
• The weather (too hot, too cold, windy, rainy, etc.),
• You were tired,
• Your eyes were strained,
• The officer was not properly trained to perform the test(s),
• The officer was inexperienced,
• The officer could not see your eyes clearly,
• The instructions were not clearly given, or
• You were wearing high heels, tight clothing or other attire that affected your ability to stand and/or walk.

Typical evidence we rely on includes your medical records, weather reports, the police’s bodycam footage, and surveillance video of the scene.

5. Other Tests

Preliminary Breath Tests

Like it sounds, the preliminary breath test (PBT) is a breathalyzer test that Colorado police administer during a DUI traffic stop. It is one of the tools that police use to determine whether there is probable cause to arrest you for driving under the influence of alcohol.

As long as you are at least 21 years old, you may decline to take this test without consequences (similar to refusing SFSTs). If you are under 21, you must submit to the PBT if the police officer reasonably suspects that you have consumed any alcohol.¹⁰

Evidentiary Breath and Blood Tests

If you are actually arrested in Colorado for driving under the influence, you will be given a choice between taking an evidentiary breath test or blood test – also called “chemical tests.” Though if the police suspect drug use, you must take a blood test since breath tests do not detect drug use.

Driving with a BAC of .08% or higher is an automatic DUI, even if you are sober. If you are operating a commercial vehicle, having a BAC of only .04% or higher is “commercial DUI.”

Note that if your BAC is above .05% but under .08%, you will likely face lesser DWAI charges. Meanwhile, drivers under 21 caught driving with a BAC of .02% to .05% will face UDD charges.

Driving with an unlawful BAC level triggers a Colorado driver’s license suspension. The length depends on your specific drunk/drugged driving case. For adults 21 and over arrested for driving with a BAC of .08% or higher, the suspension period is:

• 9 months for a first DUI,
• 1 year for a second DUI, and
• 2 years for a third or subsequent DUI.

However, you can usually drive during your license revocation period as long as you have an ignition interlock device (IID) in your car. For a first-time DUI, you can even get your IID removed after only four months (rather than nine) as long as you are fully compliant and did not have a BAC of .15% or higher.¹¹

Chemical Test Refusals

Unlike SFSTs and the PBT, evidentiary breath and blood tests are mandatory in Colorado following a drunk/drugged driving arrest.

By you choosing to drive, the law deems that you give your “express consent” to submit to these tests. In fact, refusing evidentiary tests triggers dire consequences:

• Colorado driver’s license suspension for 1 year, though you may continue driving after 60 days with an IID-restricted license,
• Designation as a persistent drunk driver (PDD),
• Driving on a IID-restricted license for 2 years,
• Mandatory alcohol/drug education and treatment program, and
• SR-22 insurance for 3 years (typically).¹²

Frequently Asked Questions

Do I have to take field sobriety tests if a police officer asks me to?

No, field sobriety tests are completely optional in Colorado. You can politely refuse to take them without any penalty. Since these tests often produce false positives and can hurt your case even when you are sober, it is generally recommended to decline them.

How accurate are field sobriety tests at detecting drunk driving?

Field sobriety tests have surprisingly low accuracy rates. The eye test (HGN) is only 77% accurate, the walk-and-turn test is 68% accurate, and the one-leg stand test is just 65% accurate. These rates are based on ideal conditions – real roadside conditions can make them even less reliable.

What happens if I refuse the breath or blood test after being arrested?

Unlike field sobriety tests, breath and blood tests after arrest are mandatory in Colorado. If you refuse, you will face a one-year license suspension, be labeled a persistent drunk driver, need an ignition interlock device for two years, and must complete alcohol education programs.

What medical conditions can make me fail field sobriety tests even when sober?

Many health issues can cause you to fail these tests while completely sober, including inner ear problems, eye diseases, diabetes, epilepsy, mobility issues, injuries, being overweight, taking prescription medications, or even fatigue and stress. Weather conditions and uneven ground can also affect your performance.

Additional Reading

For more in-depth information on field sobriety tests, refer to the following:

• National Highway Traffic Safety Administration (NHTSA) manual on standardized field sobriety tests – Detailed information about how police test suspected drunk/drugged drivers.
• Evaluation of Field Sobriety Tests for Identifying Drivers Under the Influence of Cannabis: A Randomized Clinical Trial – A JAMA Psychiatry article about how many sober drivers fail SFSTs.
• Field Sobriety Tests and THC Levels Unreliable Indicators of Marijuana Intoxication – National Institute of Justice article on the unreliability of SFSTs.
• Gaze‐evoked nystagmus induced by alcohol intoxication – A J Physiol. article on how alcohol affects eye movements.
• The Drug Evaluation and Classification (DEC) Program – A course for members of the National District Attorneys Association about how drug recognition experts (DREs) work.

See our related article about Colorado DUI checkpoints/sobriety checkpoints.

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