The Hidden Flaw in Field Sobriety Testing: Why NHTSA’s “Standardized Criteria” Do Not Actually Exist

Field sobriety tests play a major role in OVI investigations. Officers rely on them to decide whether to arrest someone, prosecutors use them to justify charges, and courts often assume they are backed by reliable science. Most people have heard of the three main tests: the Horizontal Gaze Nystagmus (HGN), Walk and Turn, and One Leg Stand. What most people do not realize is that these tests are only validated when they are performed under strict, standardized conditions.

According to the National Highway Traffic Safety Administration (“NHTSA”), the tests are supported by research only if:

1. The tests are administered in a standardized manner as instructed;

2. Standardized clues are used to score performance; and

3. Standardized criteria are used to interpret the results.

   
   

That third requirement looks simple. It appears repeatedly throughout the NHTSA manual. Courts, officers, and prosecutors all rely on it. But there is one major problem: NHTSA never defines what “standardized criteria” actually are. And that flaw opens the door to one of the most powerful cross-examination strategies in OVI defense.

The Myth of Standardization

The foundation of NHTSA’s field sobriety testing program is the idea that officers can eliminate personal judgment through standardization. That sounds reassuring. Standardization suggests consistency, reliability, and fairness.

But field sobriety testing is not nearly as scientific as prosecutors claim. NHTSA tells officers that the tests are only validated when three specific things happen:

• The officer administers the test according to the standardized procedures

• The officer uses the standardized clues

• The officer interprets the results using standardized criteria

  
  

The first two are clearly stated in the manual. The “standardized clues” are listed in detail. The step-by-step administration instructions are spelled out. The third requirement, standardized criteria, is mentioned many times but never defined anywhere in the manual, not once. This means officers are required to use criteria that do not actually exist, which leads to one unavoidable reality: their interpretation of field sobriety tests is based on discretion, not science.

The Cross-Examination Trap: What Officers Cannot Answer

When officers testify about field sobriety tests, they almost always speak with confidence. They are trained to believe the tests are scientific and repeatable. But cross-examination reveals a different story.

Defense attorneys often walk officers through the following points:

Step 1: Confirm their training. Officers acknowledge they were trained with the NHTSA manuals and understand these manuals are the national standard.

Step 2: Lock in the language. They confirm that the manual requires:

• Standardized administration

• Standardized clues

• Standardized criteria to interpret performance

Officers readily agree because this is what they were taught.

Step 3: Ask the question that breaks the illusion. “Officer, what exactly are the standardized criteria NHTSA requires you to use?” This is where everything stops.

Officers give one of three answers, and all three are damaging to their credibility:

How Officers Respond and Why Each Answer Fails.

1. “The standardized criteria are the clues.”

But the manual clearly separates the terms:

• “standardized clues” are listed in the second requirement

• “standardized criteria” appear separately in the third requirement

  
  

If they were the same thing, NHTSA would not treat them as distinct. This answer demonstrates a misunderstanding of the officer’s own training.

2. “The criteria are whatever I was taught during training.”

This shifts interpretation from science to personal judgment. NHTSA requires written, standardized criteria, not individualized beliefs. If the officer cannot identify them in the manual, then they are not standardized.

3. “I don’t know.”

This is the most honest answer, and the most devastating. Officers routinely arrest people based on tests that, by NHTSA’s own terms, are only validated when interpreted using criteria they cannot identify. That means their scoring is subjective, not scientific.

Why This Matters in an Ohio OVI Case

Ohio courts expect reliability when the State introduces evidence. Field sobriety tests are only as reliable as the officer’s ability to follow the science behind them. If officers cannot point to the very criteria that NHTSA says are necessary for validation, then the “science” collapses.

This exposes three major problems:

• Officer discretion replaces standardization

• The scoring process is inconsistent across officers

• The tests no longer qualify as validated under NHTSA standards

When the foundation is unreliable, the interpretation becomes unreliable, and unreliable evidence should not be used to support an arrest or conviction.

How a Skilled OVI Attorney Uses This to Protect You

A knowledgeable defense attorney can:

• Challenge the officer’s understanding of the manual

• Demonstrate that the required “standardized criteria” do not exist

• Show that the officer’s interpretation was subjective

• Undermine the validity of the tests

• Challenge probable cause for arrest

• Push to suppress the field sobriety tests entirely

  
  

This strategy is powerful because it does not attack the officer personally. It attacks the gaps in the scientific foundation they rely on.

Conclusion: When “Standardization” Isn’t Standard at All

Field sobriety tests are only as reliable as the rules behind them. And when officers cannot identify the “standardized criteria” they are required to use, the reliability falls apart. That is why no one should face an OVI charge without an attorney who understands NHTSA manuals, officer training, and the flaws built into these tests.

If you or someone you know is facing an OVI charge in Ohio, Harmony Law can help. I will review every aspect of your case, including the officer’s training, the administration of the tests, and whether the evidence truly meets NHTSA’s scientific standards.

Contact Harmony Law today to schedule a consultation and protect your future.