Understanding Field Sobriety Tests

Each case is fact specific, and while we attempt to describe individuals’ rights in general, we are not your lawyers and nothing stated on this website is intended as legal advice to you.

Whether or not a driver consents to perform field sobriety tests is often pivotal to the successful outcome of a case. Our experience is that those who exercise their right to remain silent and refuse to perform field sobriety tests are more likely to be found not guilty, and more likely to have their case successfully resolved even before going to trial.

When a driver tries to be cooperative with the officer and does what he/she requests, it is disheartening to later hear a judge say, “he/she did not have to perform these tests, but he/she rested on his/her rights and performed them.”

The Truth Behind Field Sobriety Tests

What are field sobriety tests? Am I required to perform these tests? What happens if I refused to perform them? (See below)

  1. What They Are – Really: You can read on if you like, or suffer from insomnia, but really, they are near acrobatic trick tests which are guaranteed for you to fail. They place people in awkward physical positions and require them to move perfectly. Also, our experience is that sobriety tests are scored extremely critically. Even if you perform the tests very well, the officer will very likely see “clues” of impairment and use the score to find probable cause for your DUI arrest.
  2. In General: Standardized Field Sobriety Tests (SFST’s) are psychophysical (a branch of psychology which studies the sensory response to physical stimuli) tests which were developed by the National Highway Traffic Safety Administration (NHTSA), a division of the United States Department of Transportation. According to NHTSA, these tests allow a properly trained officer to assess a suspect’s mental and physical impairment by having the subject perform physical exercises and scoring the subject’s performance. According to NHTSA, these tests focus on the abilities needed for safe driving: balance, coordination and information processing.

The NHTSA field sobriety training manual instructs officer/trainees that “Psychophysical testing actually begins as soon as you come into face-to-face contact with the suspect and begin the interview. Psychophysical testing continues as the suspect steps from the vehicle, and you observe the manner of the exit and walk from the vehicle. The most significant psychophysical tests are the three scientifically validated structured tests that you administer at roadside.” NHTSA’s SFST STUDENT MANUAL, 2004

The Four Main Field Sobriety Tests


a. PBT The Preliminary Breath Test

The portable, preliminary breath testing device is one which the officer may carry in his/her squad car. The device measures the BAC (breath alcohol content) of the driver.
It is not an evidentiary instrument, which means the result cannot be used in court as evidence of the BAC result shown at the time of the test. However, it can be used in court to determine whether the officer correctly determined that he/she had probable cause for the DUI arrest.

Under the Illinois DUI law, you have the statutory right to refuse this test. Drivers should exercise that right and refuse the PBT test.

b. HGN – Horizontal Gaze Nystagmus Test

Horizontal Gaze Nystagmus (HGN) refers to the involuntary jerking of the eyes when the eyes gaze to the side. According to the NHTSA, as a person’s alcohol concentration increases, the eyes will begin to jerk sooner as they move from side to side.

In addition to alcohol, there are many physical conditions which cause an increase in HGN. At best, according to NHTSA, the HGN test is 77 percent accurate.

The Illinois Supreme Court has ruled that HGN results may be admitted as evidence of intoxication, but only if the officer who gave the test is properly trained according to NHTSA standards, and gave the test properly. Because of the difficulty and numerous conditions and strict procedure required for a valid HGN test, this test has been problematic for many officers to give properly. Most officers fail to perform the test according to NHTSA protocol, and some are not properly trained. An experienced attorney knows how to challenge the HGN tests.

Test Procedure And Scoring

In the HGN test, the officer requires you to follow the motion of a small stimulus with the eyes only, keeping your head straight. The officer moves the stimulus in a particular manner to the left and right. The stimulus may be the tip of a pen or penlight, an eraser on a pencil the officer’s fingertip. There should be no lights flashing or reflecting in the background.

The officer should always begin with your left eye. According to NHTSA, the officer should examine for three specific clues of intoxication.

1. As the eye moves from side to side, does it move smoothly or does it jerk noticeably?

2. When the eye moves as far to the side as possible and is kept at that position for several seconds, does it jerk distinctly?

3. As the eye moves toward the side, does it start to jerk prior to a 45-degree angle?

According to NHTSA, if four or more clues are present, the test is 77 percent accurate for impairment from alcohol intoxication.

c. The Walk And Turn Test

The Walk and Turn test is a “divided attention” test. According to NHTSA, “divided attention” tests demonstrate that you are capable or incapable of the same mental and physical abilities that a person needs to drive safely.

The test consists of two parts, the Instruction Stage and the Walking Stage.

Instruction Stage:

In the Instructions Stage, you must stand with your feet in heel-to-toe position, keep your arms at your sides, and listen to the instructions. The Instructions Stage divides your attention between a balancing task (standing while maintaining the heel-to-toe position) and an information processing task (listening to and remembering instructions).

Walking Stage:

In the Walking Stage, you take nine heel-to-toe steps, turn in a prescribed manner, and take nine heel-to-toe steps back, while counting the steps out loud, while watching your feet. During the turn, you keep your front foot on the line, turn in a prescribed manner, and use the other foot to take several small steps to complete the turn. The Walking Stage divides your attention among a balancing task (walking heel-to-toe and turning); a small muscle control task (counting out loud); and a short-term memory task (recalling the number of steps and the turning instructions).

Scoring: Officers administering the Walk-and-Turn test observe the suspect’s performance for eight clues:

– Can’t balance during instructions
– Starts too soon
– Stops while walking
– Doesn’t touch heel-to-toe
– Steps offline
– Uses arms to balance
– Loses balance on the turn or turns incorrectly
– Takes the wrong number of steps

According to NHTSA, research shows that if a person exhibits two or more of the clues, or cannot complete the test, his/her BAC is likely to be above 0.10. According to NHTSA, this test has been shown to be accurate only 68 percent of the time.

The Juggling Test. In the Juggling Test, the officer will hand you three red balls.

(just kidding)

d. The One-Leg Stand Test:

The One-Leg Stand Test is the final NHTSA validated test. It also consists of two stages, the instruction stage and the Balance and Counting Stage:

Instruction Stage:

In the Instruction Stage, you must stand with you feet together, keep your arms at your sides, and listen to instructions. The process divides your attention between a balancing task (maintaining a stance) and an information processing task (listening to and remembering instructions.)

Balancing And Counting Stage:

In the Balance and Counting Stage, you must raise one leg, either leg, with the foot approximately six inches off the ground, keeping your raised foot parallel to the ground. While looking at the lifted foot, you must count out loud in the following manner: “one thousand and one”, “one thousand and two”, “one thousand and three” until told to stop. Typically, this will go on for 25 to 30 counts or until the officer scores at least two clues of intoxication.


While you are performing the test, the officer will score based on four clues of intoxication:

– sways while balancing;
– uses arms to balance;
– hopping
– puts foot down.

If there are two (2) or more clues detected, NHTSA says that you have a BAC of .10 (The legal limit when the tests were validated) According to NHTSA, this test is accurate only 65 percent of the time.

You May Refuse To Complete Tests

No, it is not a crime to refuse to perform the Field Sobriety Tests. Performing the tests is against your interests and will likely be used to arrest you for DUI. The tests put people in an unnatural position and ask them to do unnatural things perfectly.

The prosecution may later say that you knew you were intoxicated. They may say that you knew you were guilty, and that’s the reason you refused. Your attorney can rebut that by explaining that you were innocent and decided to decline the tests by exercising the rights of an innocent person.

The Consequences Of Refusing Tests

Although there has been legislation introduced as late as 2003 which would suspend the drivers license of any person who refused to perform field sobriety tests, to date, that legislation has been defeated. Your driver’s license will not be suspended just because you refused to perform field sobriety testing. However, your license will be temporarily suspended if you are arrested for DUI whether or not you perform the Field Sobriety Tests. Worse yet, your drivers license will be revoked, not just suspended, if you are convicted of DUI. Attempting to take the Field Sobriety Tests makes that more likely.

When, and if, your case goes to trial, your refusal to take the Field Sobriety Tests may be allowed into evidence, and the prosecution will claim it to be some evidence of consciousness of guilt — that you knew if you took the tests that you would fail. An experienced attorney can easily rebut that argument.

Contact Us For Experienced Counsel

If you were charged with DUI, call Gullberg Law, LLC, at 309-734-1001 for the experienced representation you need. You may also contact us online to schedule your initial consultation.

To learn more about DUI charges, visit our page with answers to some of our clients’ most frequently asked questions.

Gullberg Law, LLC

Gullberg Law, LLC