DUI Testing

DUI Tests: What They Do, What They Are, and When You Can Refuse Them

It is a common sight on many weekends after the bars close. Flashing lights by the side of the road, dour police leaning on cruisers, some poor guy standing in the cold with his arms extended. It’s the field sobriety test. Everyone fears it, but what are the police doing when they make a driver stand on one foot or recite the alphabet backward?

The Field Sobriety Test

The National Highway Transportation Safety Association (NHTSA) developed the field sobriety test (FST) in the late 1970s, after extensive research on what constitutes drunk or impaired driving. The FST was devised as a method to allow police to establish probable cause to believe that a driver is impaired.

The field sobriety test does not determine that the driver is inebriated. Only a blood alcohol test or a breath test can determine that. The FST is only used as a method of deciding if a driver meets the threshold to invoke the implied consent law.

Based on their research, the NHTSA determined that a blood-alcohol level of .08% was the average level at which a driver becomes too intoxicated to safely operate a motor vehicle. At that level, a person taking the tests will display certain markers that suggest they are intoxicated. This allows an officer to place them under arrest and obtain a blood test.

Implied Consent, Probable Cause, and What it Means for You

All fifty states have an implied consent law written into their driving laws. All licensed drivers consented to take a DUI test at any time when requested to do so by a law enforcement officer upon being granted a driver’s license. Refusal to take the test is grounds for suspension of your driver’s license. This information is provided on the state DMV site, and in the literature included with each driver’s license renewal form.

Beginning in 1957 with the landmark case Breithaupt v. Abram, 352 U.S. 432 (1957), the Supreme Court has continuously upheld these laws as constitutional, based on the need for public safety. Subsequent courts have broadly held that providing a blood or breath sample subsequent to a lawful arrest based upon probable cause established by a field sobriety test does not violate a subject’s Fourth or Fifth Amendment rights.

The purpose of the field sobriety test is to determine if there is probable cause to arrest a subject so that a blood or breath sample may be obtained. “Probable cause” is defined as sufficient reason based upon known facts to believe a crime has been committed or that grounds exist for a warrant to be issued. Probable cause requires facts beyond “reasonable suspicion”, but less than direct evidence.

Once you have failed to adequately perform on the field sobriety test, the officer will have sufficient probable cause to request a preliminary breath test to establish grounds for a blood test. Very recent Supreme Court decisions (Missouri v. McNeely, 569 U.S. 141 (2013) have held that unless there are exigent circumstances that prevent it, a warrant must be obtained for a blood test.

The Tests You Shall Not Pass

The field sobriety tests are intentionally difficult to pass and are meant to verify whether the individual is able to listen to instructions, carry out those instructions, and can remember instructions, while also performing the physical actions. The important part of the test is the ability to multitask.

Horizontal Gaze Nystagmus. The NHTSA recommends performing this test first. The subject is asked to follow the movement of a pen with their eyes. The officer is looking for involuntary twitches or “nystagmus” of the eyeball as it tracks left and right. In intoxicated individuals, the eyeball does not track smoothly.

A more recently developed test, vertical gaze nystagmus, can test for impairment caused by drug use. There is currently no NHTSA standard for impairment or intoxication due to cannabis or any other drug. Either one is high, or one is not.

Walk-and-Turn. For this test, the officer will ask the subject to walk nine heel-to-toe steps along a straight line, turn, then walk nine return steps. The officer is looking for swaying, using the arms for balance, but most importantly failure to follow instructions. The most common causes of failure are starting or stopping too soon, too few or too many steps, and arguing over what constitutes a straight line.

One Leg Stand. The officer asks the subject to stand on one foot and extend the other foot six inches off the ground. They then must count until instructed to stop. The officer is looking for swaying, hopping, and putting the foot down.

Limitations of the Field Sobriety Test

Despite the prevalence of their use, and acceptance by the courts, field sobriety tests have many flaws:

  • They are highly subjective. Failure or passing is entirely at the discretion of the officer giving the test.
  • Difficulty with the tests may be related to physical issues. Studies have suggested that problems executing the walk-and-turn test may stem from obesity, inactivity, or age.
  • Adverse testing conditions (darkness, cold, rain) can affect the test outcomes.

The entire purpose of the FST is to obtain probable cause that the driver is intoxicated or impaired. The FST is voluntary, and drivers do not have to agree to take the test, but police are not required to inform drivers of this fact. People v. Cooper (July 18, 2019, No. B286201) ___Cal.App.5th___ [2019 Cal. App. LEXIS 648] established that taking a field sobriety test does not violate the subject’s Fifth Amendment rights.

The Breathalyzer and Blood Test

The only real way to determine if a driver is intoxicated is by using a Breathalyzer, which tests how much alcohol is being exhaled by the person. Through a series of chemical analyses, it is possible to determine the blood-alcohol level based on the percentage of alcohol in the exhaled breath.

There are several types of Breathalyzers used in DUI testing. The handheld devices used by police during traffic stops are not considered accurate enough to be used for evidentiary purposes. An evidential reading may only be obtained with a standardized Breathalyzer at the police station.

The most reliable method of determining the blood alcohol level is through an actual blood test. The blood is drawn and then passed through a gas chromatograph/mass spectrometer. This provides an accurate percentage of the alcohol level in the blood at the time of the draw.

Refusing the Test

  • Field Sobriety Test. The FST is always voluntary. If you prefer not to stand by the side of the road holding your foot up in the air, you may immediately agree to the Breathalyzer if you choose.
  • Breath Test. If the police have enough probable cause to arrest you, they will ask you to take a preliminary Breathalyzer test. You can refuse this if you wish; but the next step is the blood test. At this point, you will be arrested and transported to jail.
  • Blood Test. At a minimum, refusing the blood test means a license suspension. Although penalties vary from state to state, you could be looking at a year or more, which is longer than a first DUI offense.


In some states, such as California, refusing a test not only has additional penalties, but it may also not help you avoid a DUI conviction. The refusal can be used as evidence you knew you were intoxicated and were trying to avoid prosecution. In Florida, a second refusal can result in up to a year in jail, and an 18-month suspension of your license.

So What to Do?

The best thing to do, of course, is not drive drunk. The next best thing is to contact your attorney and ask them to help you. All these tests are rebuttable, meaning they can be challenged in court. If you find yourself by the side of the road with flashing lights in your rear-view mirror, remember that the worst thing you can do is argue with the police over what constitutes a straight line.

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