Police Mistakes During Field Sobriety Tests Can Affect Your DWI Case

Many people assume that field sobriety tests provide an objective way to determine whether someone is intoxicated. Television and movies often portray these tests as straightforward, scientific exercises that clearly separate sober drivers from impaired ones. The reality is more complicated.

Field sobriety tests were designed to be administered using very specific procedures established by the National Highway Traffic Safety Administration (NHTSA). Those procedures exist because the tests were validated under controlled conditions using standardized instructions. When an officer departs from those standards, the reliability of the results can change significantly.

When I defend someone charged with DWI, I do not simply look at how many clues the officer recorded on a field sobriety test. One of the first things I examine is whether the officer administered the test correctly in the first place.

Field Sobriety Tests Must Follow Standardized Procedures

The three standardized field sobriety tests commonly used in Texas are the Horizontal Gaze Nystagmus test, the Walk-and-Turn test, and the One-Leg Stand test. Each has detailed instructions governing how the officer should explain, demonstrate, and score the exercise.

Those instructions are not suggestions. They are part of the testing protocol used to establish the reliability of the tests. If officers choose to skip steps, alter the instructions, or administer the test differently than they were trained, the results may no longer have the same level of reliability.

That is why I compare an officer's performance against the same training materials used to certify law enforcement officers.

The Walk-and-Turn Test Is More Complicated Than It Appears

The Walk-and-Turn test often looks simple from the outside. A driver is asked to take a series of heel-to-toe steps, turn in a specific manner, and walk back. Because the test appears straightforward, many people assume mistakes automatically indicate intoxication.

That assumption ignores how the test is supposed to be administered.

According to standardized procedures, the officer should explain each part of the test while demonstrating it. The driver is expected to watch and listen at the same time so they understand exactly what is being requested.

The officer is also supposed to ensure the driver does not begin before being instructed to do so. The standardized process includes repeated warnings designed to reduce the likelihood that a sober person starts too early simply because they misunderstood the instructions.

When these procedures are not followed, it becomes much more difficult to determine whether a driver's mistakes resulted from impairment or confusion.

How Officers Sometimes Deviate From Their Training

One issue I frequently see when reviewing body camera footage is officers giving lengthy verbal instructions before demonstrating the exercise.

Imagine trying to teach someone to tie a shoe by explaining every step first and only demonstrating the process after finishing the explanation. Most people would have difficulty remembering everything they had just heard.

Field sobriety tests work the same way. The standardized training calls for instruction and demonstration together because that method is easier to understand. When officers instead deliver a long series of verbal directions before showing the driver what to do, confusion becomes much more likely.

I also review whether officers properly explained when the test begins. If someone starts too early because the instructions were unclear or incomplete, that behavior may say more about how the test was administered than about whether the person was impaired.

The Validation Studies Assume Officers Follow the Rules

Supporters of standardized field sobriety tests often point to validation studies showing that the tests can help officers identify impaired drivers.

An important detail is sometimes overlooked.

Those studies assume that officers administer the tests exactly as they were designed. Researchers did not validate every possible variation of the instructions. They validated a specific procedure delivered in a specific way.

If an officer changes that procedure, the assumptions underlying those studies become less certain. That does not automatically invalidate the test, but it raises legitimate questions about how much confidence should be placed in the results.

When preparing a DWI defense, I compare the officer's conduct to the standardized procedures rather than simply accepting the conclusions written in the police report.

Stress Can Affect Performance

Another factor that deserves consideration is the environment in which field sobriety tests occur.

Validation studies are generally conducted in controlled settings where participants understand they are taking part in research. A roadside DWI investigation presents a very different situation.

Drivers may be standing on the shoulder of a busy highway at night with emergency lights flashing around them. They know they could be arrested. Many are nervous even if they have consumed little or no alcohol.

Stress alone can affect concentration, balance, memory, and coordination. While nervousness does not excuse poor performance, it is one of many factors that should be considered before concluding that every mistake demonstrates intoxication.

That is why field sobriety tests should never be viewed in isolation.

Video Often Reveals More Than the Police Report

One of the first pieces of evidence I request in a DWI case is the body camera and dash camera footage.

The police report summarizes the officer's observations, but the video allows me to evaluate exactly how the tests were administered. I look for whether the instructions were complete, whether the demonstrations matched the standardized procedures, and whether the driver's performance is consistent with the officer's written description.

Sometimes the video supports the officer's report.

Sometimes it raises additional questions.

Without reviewing the recordings, it is impossible to know whether the written report accurately reflects what actually occurred during the investigation.

Every DWI Case Deserves an Independent Review

Field sobriety tests are only one part of a DWI investigation. They should be considered alongside body camera footage, dash camera recordings, witness statements, chemical test results, and every other available piece of evidence.

I do not assume the officer administered the tests correctly simply because the police report says they did. I verify that by reviewing the available evidence and comparing the officer's actions to the standards they were trained to follow.

Every DWI case is different. The strength of the evidence depends not only on what the officer observed but also on whether the investigation was conducted according to established procedures.

Talk With a McKinney DWI Defense Attorney

If you have been arrested for DWI in McKinney, Collin County, or the surrounding areas, the field sobriety tests are only one part of your case. Before deciding how to proceed, the investigation should be reviewed carefully to determine whether officers followed standardized procedures and whether the evidence supports the charge.

I evaluate every DWI case by reviewing the police report, body camera footage, dash camera recordings, chemical test results, and other available evidence. That independent review helps determine the strengths and weaknesses of the State's case before important decisions are made.

Contact my office to schedule a confidential consultation.