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Field Sobriety Tests

Officer and Person conducting field sobriety tests

Field Sobriety Tests (“FSTs”) are a series of exercises designed to test for physical and mental impairment during the course of a DUI investigation. While not always the easiest to perform, law enforcement relies heavily on FSTs in order to prove a person was under the influence while driving.  

On this page we will examine the most common FSTs that are used by law enforcement as well as the accuracy of these tests.

How accurate are Field Sobriety Tests?

If you search the web regarding the accuracy of field sobriety tests you will find many different answers with some indicating that FSTs are as accurate as 91% of the time and as low as 30% of the time.  However, each of the FSTs described below has an accuracy of approximately 80% of determining whether the driver has a blood alcohol level of .08%.

Standardized Field Sobriety Tests

The National Highway Transportation Safety Administration (NHTSA) has endorsed three FSTs for use in determining alcohol impairment.  These are the horizontal gaze nystagmus (HGN), walk and turn, and the one-leg stand.

Horizontal Gaze Nystagmus

The HGN is a test where the officer will be watching for an involuntary jerking of the eyes.  The eyes have a natural tendency to do some jerking when the eyes move from side to side. However, when a person has consumed alcohol the movement will become exaggerated.  During the administration of the test, the officer is going to be looking for three clues in each eye. 

The first clue involves the ability to track. The officer will be watching to see if the eyes smoothly follow a stimulus, such as a pen when moved from side to side. 

The second clue the officer is looking for is if eye jerks at maximum deviation. The officer will move the stimulus to the left or right just outside of your vision, forcing your eyes to go to the corner.  When they do so, the belief is that if a person has consumed alcohol then the eyes begin to jerk slightly as they are working to adjust.


The third and last clue has to do with jerking within 45 degrees of center. The officer will move the stimulus until they reach approximately 45 degrees from the center to see if there is an onset of the eye starting to jerk.  The officer will then repeat this for the other eye.


The belief is that based upon a finding of 4 out of 6 clues, that the person has a blood alcohol level of at least .08%.

However, the test does not account for natural nystagmus or other eye related issues that can occur.  For instance, in a case prosecuted by Kevin, the officer found all 6 clues on the HGN and claimed that this showed the driver had a .08% or higher BAC.  However, the blood test later revealed the driver had a .03% BAC.


Walk and Turn


The walk and turn test is a divided attention test.  Divided attention tests are designed to mimic the requirements of driving.  If you think about all the things you are doing while driving (or should be doing) you are using your feet to operate the pedals, your eyes to check the mirrors, monitoring your gauges, you are judging gaps between you and other cars, you're navigating to your destination, and you may even be playing with your phone.


The first part of the walk and turn will be the instruction. The officer is going to explain the instructions and evaluate whether you were able to follow them correctly. The officer is going to instruct you to walk nine steps out, heal to toe, walking in a straight line.  At the end of the nine steps, you are to keep your foot planted, then use your other foot to make small steps to rotate yourself back around. You will then walk nine steps back to the start point, heal to toe.  During the test you are to count out loud each of your steps.


During the test, the officer is monitoring clues such as your balance, your ability to maintain a straight line, whether you maintain your feet in a heal to toe manner, whether you make the proper turn, and whether you count out loud.

According to the NHTSA, poor performance on the walk and turn correlates to a BAC of .08% or higher at least 79% of the time.


The One-Leg Stand

The one-leg stand test is another divided attention test.  During the one-leg stand the officer will instruct you to raise your foot approximately six inches off the ground and hold that position.  The officer will then tell you to count out loud using the 1001, 1002, sequence, up to 1030.  During the test, you will look at your foot.


The officer will be looking to see if you sway, hop, use your arms for balance, or if you put your foot down.  The officer will also be watching to see if you properly follow the instructions.


According to the NHTSA, the one-leg stand has an accuracy of determining a person with a .08% BAC or higher of 83%.

Non-Standardized Field Sobriety Tests

Although not approved by the NHTSA, there are law enforcement agencies that use other FSTs in DUI investigations.  There is little to no correlation between these tests and a persons BAC as well because they are not regulated, the administration can vary greatly between agencies and even individual officers from the same department.


Hand Pat Test


The hand pat test is another divided attention test that requires the driver to pat one side of their hand while the other is counting.  The officer will tell the driver to place one hand with their palm up out in front of them.  The driver will then place their other hand directly on top.  The top hand then will begin to pat the bottom hand. While doing this, the driver should be “flipping” their top hand over and then back between each pat. 


During the test, the officer will be watching to see if the driver followed instructions, ability to count correctly, and the ability to rotate hand.


If this test sounded complicated from the instructions above, imagine trying to perform this in front of law enforcement on a dark roadside or on a busy highway.


Finger to Nose Test


The finger to nose is the classic test that most people believe is an actual field sobriety test. However, it is not approved by the NHTSA. During the finger to nose, the officer will have the driver hold their arms out to their side. The driver will then bring their index finger to the tip of their nose while their head is tilted back and their eyes are closed. The driver will repeat this test three times for each side.

During this test, the officer is looking to see the driver’s ability to follow directions, swaying, tremors, muscle movement, depth perception, and whether the driver can actually touch their nose.


Rhomberg Balance Test


The Rhomberg is a favorite among Northern California agencies, especially CHP, even though it is not approved by the NHTSA.  The Rhomberg test requires the driver to stand with their feet together, tilt their head back, close their eyes, and estimate the passage of 30 seconds.  When 30 seconds has passed, the driver is supposed to open their eyes and say stop.


During this test, the officer is monitoring the driver’s internal clock. The officer is watching to see if the driver accurately stops at 30 second, whether the driver sways, eye tremors, and overall ability to follow instructions.  The Rhomberg is a favorite among alcohol and drug DUI investigations because it is believed that if a person fails to stop at 30 seconds and continues to go for a minute or more then that person is under a depressant. Whereas a person who stops the test in a few seconds is considered to be under a stimulant because their internal clock is moving fast.

What conditions affect the accuracy of Field Sobriety Tests?

While the determination of a field sobriety tests accuracy is done in a laboratory-controlled environment, the fact is field sobriety tests are rarely performed in such a manner by law enforcement.  Kevin has personally seen field sobriety tests administered in busy parking lots and even along I-80 at midnight.

There are a variety of factors that can affect the accuracy of field sobriety tests.  Such things can include the conditions under which the tests were given.  Ideally, the field sobriety tests should be conducted on a dry, hard, level surface with decent lighting.

If these cannot be performed in such conditions, the officer may move the driver to a location in order to administer the test properly.

Do I have to take Field Sobriety Tests?

No. If you are requested to take field sobriety tests you should remain calm and polite, but you should decline.  Absent FSTs, a DUI case can be very difficult to prove.

You may be tempted to perform the FSTs in order to try and show that you are not under the influence. The fact is that FSTs can be difficult to perform when you are sober. 

How to challenge Field Sobriety Tests?

There are many ways to challenge the accuracy of FSTs and a skilled and experienced defense attorney can assist in this area.  Often, the defense will attack the tests based upon the physical or mental condition of the driver.  There are a number of reasons why a person may perform poorly on FSTs such as age, illness, physical impairments, nervousness, disabilities, and mental impairment.

Other ways to attack the FSTs goes to the way they were administered.  Imagine trying to conduct the walk and turn or the one leg stand while wearing six-inch heels while standing on the side of a busy highway.  That alone makes you begin to doubt the accuracy of the test performed.  The lighting or environment is a huge factor in the accuracy of field sobriety tests, such as if it is slippery or wet, or if the officer is asking you to perform the tests in a gravel area.

Dedicated DUI Attorney

Kevin Ballard is a dedicated DUI attorney based in Fairfield who understands how to effectively defend those charged with DUIs. Kevin is one of the few attorneys who is both a former prosecutor and trained as a police officer. As such, Kevin knows first hand how DUIs are handled from the initial traffic stop through prosecution and appeal. Let the Law Office of Kevin L. Ballard help you today defend your rights and protect your liberty.

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