Field sobriety tests (FSTs), along with breathalyzer test results, are the evidence that prosecutors rely on most to get DUI convictions, but how do they work, and are they reliable?

Cops and prosecutors would like jurors to believe that field sobriety tests are a reliable, scientific method of determining whether a person’s blood alcohol content (BAC) is greater than .08. But are they?

How do field sobriety tests really work?

Below, I’ll discuss what field sobriety tests are and how they are used in DUI cases in SC, including:

• Whether field sobriety tests are reliable,
• The difference between standardized and non-standardized FSTs,
• How to defend against field sobriety tests in court, and
• The types of field sobriety tests used by SC law enforcement.

Are Field Sobriety Tests Reliable for Determining BAC?

What are field sobriety tests?

They can be an effective tool for prosecutors to prove that a person was intoxicated in a driving under the influence case, but, despite their admissibility in court, they are not a reliable indicator of a person’s BAC.

So why are they admissible in court?

Because they work – jurors want to believe prosecutors and cops, and the illusion of a “scientific” test that tells us whether a person was intoxicated is believable and persuasive for most jurors. Prosecutors, cops, judges, and even many jurors want convictions, and FSTs give them something to hang their hat on to say a person is guilty.

But are they reliable, really?

According to studies conducted by NHTSA, the three standardized FSTs are 91% accurate. Of course, this assumes the officer is properly trained in the administration of the tests, the officer is being objective while administering the tests, all three tests are administered together, and the subject doesn’t have health problems that would affect their performance like:

• Back problems,
• Leg or knee problems,
• Soreness from driving for hours,
• Vertigo or other balance issues,
• Medical nystagmus,
• Weight issues, or
• Literally hundreds of medical issues that can affect a person’s performance on the FSTs.

How do Field Sobriety Tests Work?

There are only three “standardized” field sobriety tests that NHTSA has approved for use.

This means that these three tests – the horizontal gaze nystagmus (HGN), one-legged stand, and walk and turn tests – have some value in determining whether a person is intoxicated, while the non-standardized tests that law enforcement still sometimes use have no value in determining a person’s intoxication level.

How does it work?

While you are performing for the officer, they look for “clues.” A certain number of clues means that you “fail” the test. The clues that cause you to “fail” may include things like:

• Not remaining perfectly still with your hands by your sides as the officer reads the instructions to you,
• Not turning exactly the way the officer instructed you to turn after taking your nine heel to toe steps in the walk and turn test,
• Stopping, even briefly, while walking the line, or
• Stopping counting before the officer tells you to stop as you are holding your foot exactly six inches in the air and parallel to the ground during the one-legged stand test.

How long do you think most sober people can stand on one foot, holding their other foot exactly six inches above the ground and parallel to the ground while counting aloud with flashing blue lights in their face as cars drive by feet away on the highway?

The bottom line is, if the officer thinks that you are DUI, you are going to “fail the test.” It is designed for you to fail and to give the State evidence to use against you when the officer thinks that you are DUI.

Is that reliable evidence? If the person performs poorly on FSTs, it could mean that they are intoxicated. It could also mean that they have health issues or just aren’t that athletic – unlike the officer who may be in top physical condition and who practices FSTs on almost a daily basis.

Does anyone “pass” field sobriety tests? Maybe, but consider 1) the test is designed so the officer can find enough “clues” to fail a sober person, and 2) if the officer didn’t think you were DUI, they wouldn’t be giving you the tests…

Types of Standardized Field Sobriety Tests in SC

The standardized field sobriety tests include the horizontal gaze nystagmus test, the one-legged stand test, and the walk and turn test.

The horizontal gaze nystagmus (HGN) test consists of the officer moving a pen or small light back and forth in front of your face as you follow it with your eyes, looking for 1) pupil size, 2) resting nystagmus (involuntary jerking of the eye), and 3) equal tracking as your eyes follow the light.

Seems reasonable – nystagmus really does happen when a person is drunk. The problem is that many other medical conditions cause nystagmus. I know more than one person who has nystagmus in one or both eyes all the time – when they are not intoxicated.

The walk and turn test consists of:

• Standing in one spot with your feet heel to toe and arms at your sides as the officer takes their time reading the instructions to you (moving at this point is a “clue” the officer will use to “fail” you),
• Taking exactly nine steps with your heel touching your toe on each step in a straight line without lifting your arms as you walk,
• Making a very specific turn at the end of the nine steps that must be performed exactly the way the officer demonstrates for you, and
• Making exactly nine steps back in the same manner.

The one-legged stand test consists of 1) standing in one spot with your feet together and your arms by your sides while the officer takes their time reading instructions to you (move and it’s a “clue” that the officer will use to “fail” you) and 2) lifting one foot exactly six inches off the ground, parallel to the ground, and holding that position while you count until the officer tells you to stop counting.

How to Defend Against Field Sobriety Tests in Court

If they will hurt your case, the most effective defense against field sobriety tests in court is to get the FSTs excluded so the jurors don’t see them – for example, if the officer did not administer the tests properly, they should be inadmissible.

On the other hand, FSTs are not always damaging evidence – if our client performed fairly well on the FSTs (despite the officer’s conclusion that they “failed”) or if there is a reasonable explanation for what would have otherwise been a poor performance, video of the FSTs could be helpful evidence in your case.

If you have legitimate medical issues that would prevent you from performing the FSTs, you should have the opportunity to explain this to the jury and present an expert witness who can testify as to your medical issues and how they would affect your performance.

Depending on the facts of your case, you may want to retain an expert on field sobriety tests who can explain to the judge or jurors 1) how the officer administered them incorrectly or 2) why you were unable to perform them correctly.

Non-standardized field sobriety tests (alphabet tests, finger counting tests, or touching your nose with your eyes closed) should be excluded from your trial (although NHTSA’s training manual says they can be used if there are reasons the officer cannot perform the standardized tests).

HGN tests are inadmissible unless they were administered in conjunction with the walk and turn and one-legged stand tests (see State v. Sullivan).

And finally, when the FSTs are not excluded from trial, it is not difficult to demonstrate how ridiculous they are as an indicator of intoxication:

• Get the officer to describe the steps for each test in detail,
• Get the officer to demonstrate each test for the jurors,
• Get the officer to acknowledge that he or she demonstrates (practices) these tests routinely – how many times a year? More or less than a hundred?
• In closing, review the officer’s testimony and the steps for each test, and
• Ask the jurors to try administering them to each other during deliberations.

Most juries are going to have one or more people who are older, who are overweight, or who have physical problems that prevent performing the tests. Hopefully, they will give it a try in the jury room and see for themselves that FSTs are a sham and not a reliable indicator of a person’s BAC.

DUI Defense Lawyers in Charleston, SC

Charleston, SC criminal defense attorney Grant B. Smaldone focuses on criminal defense and criminal trial practice in the Charleston, Dorchester, Georgetown, and Myrtle Beach areas of South Carolina.

If you have been charged with a crime, call now at (843) 808-2100 or get in touch online to talk to an experienced SC defense lawyer today.