​What Are Field Sobriety Tests?

What Are Field Sobriety Tests?

If you’ve ever been pulled over on suspicion of drunk driving, you’ve probably heard of field sobriety tests. But what exactly are they and how do they work? Keep reading to get the full scoop on these commonly used tests.

Purpose of Field Sobriety Tests

Field sobriety tests are a battery of tests used by police officers to determine if a driver is impaired by alcohol or drugs. They are conducted roadside, after a driver has been pulled over on suspicion of DUI. The officer will instruct the driver to perform a series of tasks designed to gauge coordination, balance, and mental agility–all things that are negatively impacted when someone is under the influence.

So in short–field sobriety tests allow officers to evaluate if a drivers faculties are impaired in a way that would make it unsafe for them to operate a vehicle. The tests also collect evidence to help support a DUI arrest.

Standardized Field Sobriety Tests

There are a few field sobriety tests that are used across the board by law enforcement agencies. These standardized tests, validated by the National Highway Traffic Safety Administration (NHTSA), include:

  • Horizontal Gaze Nystagmus Test
  • Walk-and-Turn Test
  • One-Leg Stand Test

Let’s break these down in more detail…

Horizontal Gaze Nystagmus Test

This test measures an involuntary jerking of the eyes as they gaze to the side.

To conduct the test, an officer has the driver follow a stimulus like a pen or flashlight with their eyes only–keeping their head still. As the eyes move from center to the periphery, the officer looks for jerking movements.

Nystagmus means a distinct and sustained jerking when the eyes are gazing at a peripheral point. Alcohol and certain other drugs can enhance this jerking, so officers take note if distinct nystagmus is observed.

Walk-and-Turn Test

This divided attention test requires the driver to listen and follow instructions while performing simple physical movements.

The driver is directed to take nine heel-to-toe steps along a straight line, while counting the steps out loud. After taking the nine steps, the driver must turn on one foot and return back down the line in the same manner.

During the instructions, the officer looks for signs that the driver cannot follow directions. During the walking stage, the officer looks for signs like using one’s arms for balance, stepping off the line, missing heel-to-toe steps, losing balance, or stopping while walking.

One-Leg Stand Test

This test requires the driver to stand on one leg while counting out loud to 30. The driver is told to raise one leg, either leg, with the foot approximately 6 inches off the ground, keeping raised foot parallel to the ground. While looking at the elevated foot, the driver then counts out loud from 1,001 until told to stop.

The officer times the 30 seconds it should take to complete the counting. The officer looks for signs like swaying, using arms to balance, hopping, putting the foot down, etc.

Nonstandardized Field Sobriety Tests

In addition to the standardized tests, officers may include some informal, nonstandardized tests as part of a field sobriety test battery. Some examples include:

  • Finger to Nose – Touching the tip of the nose with a finger to test hand-eye coordination.
  • Alphabet Test – Reciting a portion of the alphabet to test speech and memory.
  • Counting Test – Counting backwards from a number to test mental agility.

While these nonstandardized tests can provide additional evidence of impairment, they are not validated by research like the NHTSA standardized tests.

Clues Officers Look For

Officers administering field sobriety tests are trained to look for specific clues that indicate impairment. Examples include:

  • Inability to follow directions
  • Using arms for balance
  • Stepping off the line
  • Swaying
  • Hopping
  • Putting foot down

The number of clues observed can help the officer determine if a driver is impaired. Generally, the more clues, the more likely the driver is over the legal limit for intoxication.

Refusing the Tests

You do have the right to refuse field sobriety testing. However, refusing looks suspicious and will likely still result in a DUI arrest if the officer already has probable cause you are impaired. Evidence of your refusal can also be presented in court.

That said, poor performance on the tests provides more solid evidence of intoxication that can be used against you. So some drivers opt to politely refuse the tests. Just know refusing comes with consequences.

Test Accuracy

How accurate are field sobriety tests? The reliability of these tests has been extensively studied. Research shows they are generally accurate and reliable when administered properly by trained officers.

However, the tests aren’t perfect. There is always a chance of false positives (failing the test when not impaired) or false negatives (passing the tests when over the limit). Accuracy is impacted by factors like weather, age, injuries/conditions, and officer variance.

Blood Alcohol Tests

Field sobriety tests are used to detect driver impairment and establish probable cause for arrest. But the real evidence of intoxication comes later at the police station (or hospital) in the form of a chemical BAC test.

These evidentiary chemical tests analyze a drivers blood, breath, or urine to determine their precise blood alcohol concentration (BAC). The legal BAC limit for driving is 0.08% in all states. So if a drivers BAC is over 0.08%, that solidifies the DUI charge.

Field sobriety tests provide the probable cause to make the arrest and request chemical testing. The BAC chemical test provides the hard evidence to prove intoxication in court.

Preparing a Defense

If you performed poorly or refused the field sobriety tests, don’t panic. There are still ways your DUI defense attorney can challenge the results in court.

For example, if the officer didn’t administer the test properly or scored your performance incorrectly, that could weaken the evidence. Factors like weather, traffic, nerves, injuries, or medical conditions could also explain poor performance.

And don’t forget–the field sobriety tests are subjective. It ultimately comes down to the officers judgment and opinion, which is up for debate. There are plenty of ways for a skilled DUI lawyer to call the results into question.

The Bottom Line

Field sobriety testing is a series of roadside tests used by officers to evaluate impairment and establish probable cause for a DUI arrest. While these tests provide helpful evidence, they are not perfect indicators of intoxication. There are still ways a strong legal defense can challenge the results in court. So don’t panic or give up hope if you performed poorly on these tests after being pulled over. Consult an experienced DUI attorney who can carefully examine the results and build an aggressive defense challenging their validity. With a seasoned lawyer on your side, you can fight the charges and work towards the best possible outcome for your case.


NHTSA Standardized Field Sobriety Test Manual

VeryWellMind – What Are Field Sobriety Tests?

DrivingLaws.org – Refusing Field Sobriety Tests in California

Reliability of Field Sobriety Tests