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A Look at the Accuracy of Field Sobriety Tests

As you might beware, driving under the influence, also commonly abbreviated as DUI, is a severe charge in the eyes of the law. Before an arrest for a DUI charge, police officers at the DUI sobriety checkpoint will require you to perform some field sobriety tests to confirm whether or not you were driving under the influence. Poor performance on these field sobriety tests will give a police officer a reason to arrest you.

However, it doesn’t mean you are guilty of the DUI charge yet because these tests are occasionally inaccurate and untrustworthy. When the police arrest you at a DUI checkpoint, it is wise to seek the services of a defense attorney immediately to protect yourself from a wrongful conviction.

Attorneys at Jonathan Franklin DUI Attorney, are ready to help you prove your innocence for the best possible outcome if you are under arrest for a DUI charge in Los Angeles, California. We will keenly evaluate the arresting officers’ evidence against you, including the field sobriety tests results, to build the best defense strategies to protect your interests for the possible result of the alleged case.

To better comprehend a DUI charge and strategies to fight it, we need to know how an arrest begins. Therefore, let us look at the accuracy of field sobriety tests and how they influence your DUI case.

Understanding Field Sobriety Tests

According to section 23152 of the Vehicle Code (VC), it is illegal to drive a motor vehicle or any automobile while under the influence of alcohol or any other controlled drug substance like marijuana. Since accidents related to DUI are catastrophic and fatal, law enforcement officers use roadside sobriety tests to enforce DUI laws and curb the rate of these accidents.

One of the sobriety tests that officers will use to gauge your level of intoxication after pointing out your vehicle pull over at a DUI checkpoint is field sobriety tests (FSTs). Field sobriety tests are typically a series of physical tests that the officers will ask you to perform after stepping out of your car to determine whether or not you are driving under the influence of alcohol or other illegal drugs.

An In-Depth Look at the Accuracy and Reliability of Field Sobriety Tests

Now that you understand what field sobriety tests are in a DUI case, you need to know how they can impact or influence your alleged DUI case. Elaborated below are various common and standard field sobriety tests the officers will require you to perform after stopping at the DUI checkpoint and their inherent accuracy issues:

The Walk and Turn Test

The walk and turn test (WAT), also commonly known as the nine-step test, is one of the standard FST you should expect after stopping at a DUI checkpoint. Typically, the WAT will divide your attention to enable the officers to determine your ability to consistently walk in a straight line, maintain balance and follow instructions. The officers will instruct you to do the following during this test:

  • Take nine heel-to-toe walking steps on a drawn or imaginary straight line on the ground
  • Keep your hands at your sides
  • Look at your steps or feet while walking on the line
  • Count out loud in a proper manner
  • Maintain your feet on the straight line
  • Turn in a particular manner after reaching the end of the line
  • Walk back to the start of the line

Even if it is your first time undertaking this test, the officer will expect you to remember all the above instructions and perform the test as a sober person would. During the WAT test, the officer will look for the following clues or indicators of intoxication:

  • Starting to soon
  • Walking out of the line or swaying
  • Your steps are not touching heel-to-toe
  • Stopping while walking
  • Making improper turns
  • Raising your hands to maintain balance

According to NHTSA (National Highway Traffic Safety Administration), the accuracy of this test in determining whether or not you are under the influence is 68%. To that end, if you exhibit two or more of any of the above indicators of intoxication, the officer has the authority to arrest you on suspicion of DUI.

Since there is a 32% chance that your performance in the WAT could be inaccurate, your attorney can challenge the officer’s evidence against you for a less severe related charge or perhaps acquittal of the charge. Lawmakers acknowledge that even a sober person can lose balance while walking on a straight line due to any of the following issues:

  • Poor weather
  • Poor terrain
  • Poor lighting
  • An inherent physical condition or injury, for example, a knee injury
  • The officer’s instructions were incorrect

One Leg Stand Test

In a one-legged stand test (OLS), the officer will ask you to stand with one foot while the other is about six inches above the ground for approximately 30 seconds. Like the nine-test step, the officer must give you instructions on what to do during this test. During the OLS test, the officer will look for the following indicators or signs of intoxication and impairment:

  • Hopping to maintain your balance
  • Raising your arms to balance
  • Swaying while balancing
  • Starting too soon
  • Lowering your foot on the ground too soon

According to NHTSA, exhibiting two or more of the above-listed signs will give the officer probable cause to arrest you because there is a 65% possibility that your BAC level is approximately 0.10% and above.

If you perform poorly on this test, it doesn’t mean you are guilty of DUI. A reliable DUI attorney can attack the arresting officer’s evidence against you and prove the inaccuracy of this test. Lawmakers acknowledge that the OLS test is prone to accuracy issues because even a sober person can perform poorly on the test due to issues that are unrelated to alcohol consumption.

For instance, if you’re wearing high-heeled shoes, it might be challenging to stand with one leg, even for 10 seconds. Balancing yourself while one foot is up in the air can be problematic even for a fit individual, especially if he/she doesn’t practice balancing often.

Typically, the following issues can affect the accuracy of the OLS test results in determining whether or not you’re under the influence of alcohol or other illegal drugs:

  • Knee, back, or hip injury
  • Your Weight
  • The ground was slippery or nonuniform
  • Inadequate lighting
  • Underlying medical conditions
  • The clothes you are wearing
  • Windy conditions
  • Improper timing

While performing this test, the officer will record a video to use against you in court. However, this piece of evidence would be inadmissible in court if your defense attorney can prove to the court the above issues were the cause of your inability to stand with one leg as instructed by the officer. If that is the situation, the court will drop or reduce the alleged DUI charge to a less severe offense.

Horizontal Gaze Nystagmus Test

The last standard FST that the officer at the DUI checkpoint will use to determine whether or not you were drunk driving is the horizontal gaze nystagmus test (HGN). Typically, nystagmus is the involuntary twitching or jerking of the eye, which occurs when you rotate your eyes at a high peripheral angle.

In the HGN test, the officer will require you to track the movement of his/her finger or a penlight slowly using your eyes. The purpose of doing this is to determine if your eyes are moving in an inconsistent jerky way, which is an indicator of impairment or intoxication.

According to NHTSA, this HGN test is 77% reliable in gauging whether or not your BAC is 0.10% or above. During the HGN test, the officer will look for the following clues or indicators of intoxication:

  • Whether or not the onset of your nystagmus is happening before your eyes are at a 45-degree angle
  • Whether or not you can follow the object or his/her finger smoothly from right to left without jerking your eyes
  • Sustained and distinct nystagmus or jerking when your eye is at a maximum deviation

Although this procedure is 77% accurate in evaluating whether or not you were drunk driving, a skilled defense attorney can challenge this accuracy to counter the alleged DUI charge against you. An experienced defense attorney can point out several weaknesses in the prosecutor’s DUI case against you for the best possible outcome.

Even if you exhibit any of the above signs of intoxication, there are several ways your defense attorney can attack and challenge the accuracy of your results in the HGN test, including:

  • The arresting officer didn’t have the proper training required to administer the test correctly as required by the NHTSA
  • The arresting officer had a challenge in estimating the 45-degree eye angle
  • The cause of the exaggerated nystagmus was due to other issues unrelated to alcohol consumption, for example:


  1. You have a head injury
  2. Particular medical conditions, like the movement of the fluid in your inner ear
  3. Particular medicines and drugs like phencyclidine
  4. You had contact lenses on
  5. Improper positioning of the penlight or any other object, acting as the stimulus

Although the NHTSA has approved the above three standard FSTs in determining whether or not a driver is driving under the influence, they are not 100% accurate. With an aggressive DUI attorney in your corner, you can attack and challenge the prosecutor’s evidence obtained at the DUI checkpoint by the arresting officers to weaken his/her case against you.

Other Sobriety Tests to Expect at the DUI Checkpoint

After completing the above standard FSTs, the officer may require you to perform other non-standard sobriety tests in an attempt to gather adequate probable cause to initiate an arrest for DUI. Other non-standard sobriety tests to expect at the DUI checkpoint include:

  • Blowing a breathalyzer
  • Counting backward
  • Reciting some sections of the alphabet
  • The Romberg balance test
  • Finger dexterity test

Although the above tests are not scientifically validated and approved by the NHTSA, it will not stop the officer from using them to determine whether or not you were driving under the influence. If you are under arrest for a DUI charge after performing poorly on these sobriety tests, you should talk with an attorney as soon as possible.

Even if you know you weren’t drunk driving, attempting to prove your innocence to the officers will not help once you are under arrest. If you are under arrest for an alleged DUI offense, you should bear in mind that you have the following vital constitutional protections:

  • Right to be free of illegal/unlawful search and seizure regardless of your race or skin color
  • Right to stop talking with officers whenever you want to or remain silent
  • Right to have a private attorney on your side or a public defender if you cannot afford one

After the arrest at the DUI checkpoint, the officers will carry you with their van to the police station for an administrative, legal procedure known as booking. Typically, during this procedure, the arresting officer will do the following:

  • Record your name, alleged DUI charge, age, and year of birth
  • Take your mugshots (passport-sized photo of you)
  • Confiscate your belonging, for example, jewelry, belts, watches, and clothing
  • Full body search
  • General medical evaluation

After this procedure, the officer will place you in jail before your first court hearing, commonly known as the bail hearing. To increase the chances of fighting the alleged DUI charge against you, you will depend on your defense attorney at every stage of the criminal justice system.

Find a Los Angeles DUI Attorney Near Me

Because of the accuracy issues inherent in these field sobriety tests, failing this test does not mean you are guilty of a DUI charge. A reliable attorney can counter the alleged DUI charge against you by pointing out these inaccuracy issues in your FSTs results to achieve the best outcome.

We invite you to call profound attorneys at Jonathan Franklin DUI Attorney at 323-464-6700 if you or your beloved friend is in police custody for an alleged DUI charge in Los Angeles, California. We understand the complexities of DUI cases in the eyes of the law and will strive to defend your rights for the best possible outcome in each stage of the criminal justice system.

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Jonathan Franklin DUI Attorney
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