Skip to Content

Why Sober Drivers Fail Field Sobriety Tests

police officer conducting field sobriety test to woman with a pen

Law enforcement began using field sobriety tests in the 1980s. These tests rely heavily on officer discretion to determine whether or not the driver’s behavior shows they are intoxicated. However, these tests get critiqued for that very reason. Let’s go over the three main types of field sobriety tests and what non-alcohol related factors may prevent you from passing.

Types of Field Sobriety Tests

One-Leg Stand Test

The driver’s ability to balance is tested during this exercise. If an officer requests you take the test, you will have to stand straight and hold one foot in the air about 6 inches off the ground. You must keep your hands at your sides and count until the officer instructs you to stop.

The main factors that the officer will be observing during this test are:

  • If you begin to sway while balancing on one foot
  • If you put your foot down before being told to
  • If you have to use your arms to maintain balance

The Walk and Turn Test

This is another balance-based test and also relies on the ability to follow directions.
The walk and turn test is likely the first that comes to mind for many people when thinking about field sobriety tests.
During this test you must:

  • Walk heel-to-toe and take approximately 9 steps forward
  • Walk in a straight line
  • After the 9 steps, pivot to turn around
  • Repeat

The officer will observe your overall balance during the test. If you cannot walk in a straight line, don’t step heel-to-toe, don’t follow all instructions, and show other indicators of impairment, the officer may determine you are intoxicated.

Horizontal Gaze Nystagmus Test (HGN)

This test doesn’t involve physically moving. Instead, it focuses on your eyes.
During this test, the officer will hold an object in front of your face, usually a pen. The officer will then tell you to follow the object with only your eyes, not your entire head. They will then slowly move the pen back and forth while they examine you.

During this, signs of impairment are usually less clear. Officers may look for:

  • Jittery eyes
  • Large pupils
  • Inability to follow the object
  • If you move your head while following the object with your eyes

Why Sober Drivers Fail

Numerous factors can lead a sober driver to fail a field sobriety test. In fact, roughly 30% of people can’t pass these tests when sober.


For a lot of people, anxiety evokes a physical response. This could be in the form of sweating, shortness of breath, shaking, numb limbs, or lightheadedness. Interacting with the police is anxiety-inducing for a lot of people, even when they have done nothing wrong.

Unfortunately, these symptoms of anxiety may be perceived as signs of intoxication.

Medical Conditions

Some medical conditions can affect your ability to complete the tasks of field sobriety tests. For example, muscle tremors can cause you to lose your balance, but the officer may believe it’s alcohol at fault.
Other conditions that can seriously impact your ability to pass a field sobriety test include:

  • Vertigo
  • Epilepsy
  • Inner ear conditions
  • Head trauma
  • Back injuries
  • Recent surgery


As crazy as it sounds, if you had a lot of caffeine that day, you may not be able to pass a horizontal-gaze nystagmus test. The caffeine stimulates your whole body and leads to jitters. Your eyes may move strangely because of this, but officers could believe it is due to alcohol or illegal drugs.


Fatigue can have a significant impact on your ability to pass a field sobriety test. If you’re fatigued from a long drive or it’s late at night, you may have difficulty focusing on or comprehending the test’s instructions.

Balancing is also difficult if your muscles are fatigued from driving for long periods. When getting out of the car you can feel your blood flowing and muscles stretching out. However, if you have to get out of the car and immediately participate in a balance-based evaluation, you will likely not give your best performance.

Dallas DWI Defense Lawyers

Scott H. Palmer, P.C. can help you fight your DWI charges after a failed field sobriety test. A subjective method of testing like this should not lead to a criminal conviction. Call us today at (214) 891-3382 to get started with our Texas DWI attorneys.