What Are Field Sobriety Tests (FSTs)?

Field Sobriety Tests (FSTs) are physical and cognitive exercises administered by police officers during a DUI stop. Their purpose? To determine whether a driver is impaired.

But here’s the reality: FSTs are highly subjective, designed for failure, and often unreliable.

If you’ve been arrested based on an FST result, it’s critical to understand what these tests are, how they work, and how they can be challenged in court.

questioned by police

The Standardized Field Sobriety Tests (SFSTs) – And Their Flaws

The National Highway Traffic Safety Administration (NHTSA) has approved three "standardized" FSTs:

1. Horizontal Gaze Nystagmus (HGN) Test

  • The officer moves a pen or finger side to side while watching your eyes for involuntary jerking (nystagmus).
  • Flaws: Fatigue, medications, bright lights, and even natural eye conditions can cause nystagmus without any alcohol involvement.

2. Walk-and-Turn (WAT) Test

  • You must walk heel-to-toe in a straight line, turn, and return. The officer watches for balance issues, incorrect steps, or stopping.
  • Flaws: Anxiety, uneven pavement, bad weather, poor footwear, or simply nerves can cause failure.

3. One-Leg Stand (OLS) Test

  • You stand on one foot while counting aloud for 30 seconds. The officer notes swaying, using arms for balance, or putting a foot down to steady yourself.
  • Flaws: People over 40 [MK2], those with knee or back pain, or anyone with even minor balance issues are at a disadvantage.

The science behind these tests is weak, and even in controlled settings, they are far from 100% accurate:

  • HGN: 77% accuracy
  • Walk-and-Turn: 68% accuracy
  • One-Leg Stand: 65% accuracy

That means that 1 in 3 sober people can "fail" an FST simply due to environmental, medical, or physical reasons.

Non-Standardized Field Sobriety Tests – Even More Unreliable

Officers sometimes use additional, even less reliable tests, including:

  • Finger-to-Nose Test: Requires touching your nose while your eyes are closed.
  • Reciting the Alphabet Backwards: At times, hard to do sober, let alone under mounting stress.
  • Counting Fingers or Steps: Tests short-term memory and coordination, not impairment.

None of these tests have scientific backing, yet they are still used to justify arrests.

The Reality of Field Sobriety Tests: Designed for Failure

If you’ve seen Steve Martin’s 1983 film The Man with Two Brains, you’re sure to remember the scene where he’s pulled over and asked to complete a ridiculously difficult sobriety test—balancing, hopping, spinning, singing, juggling, and, finally, catching a fly with chopsticks.

It’s satire—but it’s not far off from reality, certainly in the view of anyone who has just been pulled over, questioned, and is performing under pressure knowing that an arrest is a possibility.

Steve Martin’s character, Dr. Hfuhruhurr, passes but, in the real world, FSTs set drivers up to fail. Officers assume impairment from the start, and any small mistake is taken as proof of DUI.

This confirmation bias plays a huge role in wrongful DUI arrests.

How Field Sobriety Tests Impact Your DUI Case

1. They Are a Key Part of Probable Cause

FSTs are often the main evidence used to justify an arrest. If the officer believes you “failed,” that alone could be enough to take you into custody—even if you pass a breathalyzer later.

2. Prosecutors Use Them Against You

If your case goes to court, the prosecution will argue that your "failure" proves impairment, regardless of the test's flaws, often regardless of what the dashcam shows.

3. They Can Be Challenged

A skilled DUI attorney can expose the weaknesses in the tests and potentially get them thrown out of court, weakening the case against you.

How a DUI Attorney Can Challenge FST Results

An experienced DUI lawyer can attack FST results in multiple ways:

  • Questioning the Officer's Training: Were they properly certified? Did they administer the test correctly?
  • Highlighting Environmental Factors: Was the pavement uneven? Were there distractions (traffic, sirens, wind)?
  • Pointing Out Medical or Physical Limitations: Do you have injuries, vision issues, or anxiety that could have affected your performance?
  • Demanding Bodycam Footage Review: Do the videos match the officer’s report, or was there bias in their observations?

Can You Refuse a Field Sobriety Test?

Yes! In Washington State, you are NOT legally required to take FSTs.

However, officers often don’t clarify this. If you refuse, they might say things like:

“ I’d like you to step out of the car and take a voluntary test just to make sure you’re safe to drive, then you can be on your way. This is usually delivered in a way that minimizes the word “voluntary” and emphasizes “I’d like you to . . . “These statements are designed to pressure you—but refusing FSTs is NOT illegal.

Pro Tip: If a police officer asks you to exit your car the odds are high that you’re not getting back in . . . you will be arrested.

What Should You Do If Asked to Perform an FST?

  • Be Polite, But Firm: "Officer, I respectfully decline to take these tests."
  • Don’t Volunteer Information: The less you say, the better.
  • Request an Attorney Immediately: A lawyer can protect your rights from the start.

Final Thoughts: Don’t Let an FST Determine Your Future

Field Sobriety Tests are flawed, subjective, and unreliable. They are not scientific proof of impairment—but they are often used that way in court.

If you’ve been arrested after "failing" an FST, you need an experienced DUI attorney to challenge the evidence and fight for your case.

Arrested for DUI? Call a Defense Attorney Now

Knauss Law knows when and how to challenge faulty Field Sobriety Tests and fight DUI charges. Contact us today - one bad test shouldn’t ruin your future.