December 21, 2023

What are the Standardized Field Sobriety Tests?

Standardized Field Sobriety Tests (SFSTs) were developed as a means to assess impairment in drivers suspected of driving under the influence (DUI). These tests have been widely adopted by law enforcement agencies across the United States, thanks to the guidelines established by the National Highway Traffic Safety Administration (NHTSA).

How SFSTs Were Developed

The development of SFSTs was based on scientific research and empirical studies. The NHTSA conducted extensive research to determine which tests would provide the most reliable indicators of impairment. Through this research, they identified three tests that have become the standard for assessing impairment in DUI cases:

  1. The Horizontal Gaze Nystagmus (HGN) test: This test measures involuntary eye movements that may be exaggerated when a person is under the influence. It is important to note that under established Tennessee caselaw, the HGN test can be excluded from trial if the person administrating the test is not a qualified expert. It is important to have an experienced criminal defense attorney who can file the proper pretrial motions to address this issue.
  2. The Walk-and-Turn test: This test assesses a person's ability to follow instructions, maintain balance, and perform simple physical movements.
  3. The One-Leg Stand test: This test evaluates a person's balance and stability while standing on one leg.

Standardized Field Sobriety Tests – Explained Further

1. The Horizontal Gaze Test (HGN)

The Horizontal Gaze Test (HGN) is a commonly used field sobriety test that helps determine if a driver is under the influence of alcohol. It does this by measuring their eye movements.

  • Observation: A police officer will ask the driver to follow a stimulus (like a pen or flashlight) with their eyes as it moves horizontally.
  • Indicators of Impairment: The officer looks for specific signs that may indicate impairment, such as:
  • Lack of Smooth Pursuit: If the driver's eyes don't move smoothly while tracking the stimulus.
  • Distinct Nystagmus at Maximum Deviation: When the driver's eyes start jerking noticeably when looking as far to the side as possible.

These indicators are believed to be more pronounced in people who have consumed alcohol.

It's important to note that the HGN test has its limitations and can be challenged in court. Some common challenges include:

  • Improper administration of the test
  • External factors (like bright lights or windy conditions) that could affect the driver's ability to perform the test accurately
  • Medical conditions or medications that might impact eye movements
  • Test not administered by trained expert (Tennessee Caselaw

If you're facing DUI charges and have undergone an HGN test, it's crucial to understand how this test works and its potential weaknesses. Consulting with an experienced criminal defense attorney can provide you with valuable insights, help identify any flaws in HGN evidence, and develop effective strategies for challenging its reliability in court.

2. The Walk-and-Turn Test

The Walk-and-Turn Test is a standardized field sobriety test used by law enforcement to assess a driver's level of impairment. This test helps determine if a person is under the influence of alcohol or drugs by evaluating their divided attention and physical coordination.

During the Walk-and-Turn Test, the driver needs to perform the following steps:

  1. Stand with your heel touching your toe.
  2. Take nine heel-to-toe steps along a straight line.
  3. Turn as instructed.
  4. Take nine heel-to-toe steps back along the same line.

The police officer will closely observe how well you follow these instructions while maintaining balance and coordination.

Procedural Errors That Can Invalidate the Accuracy of the Walk-and-Turn Test

Several factors can affect the accuracy of the Walk-and-Turn Test:

  • Environmental conditions like uneven terrain or poor lighting.
  • Certain medical conditions or physical impairments that may make it difficult for you to perform the test correctly.

These factors can lead to potential misinterpretation of the results by law enforcement, making it important to understand how they may impact your case.

Challenging the accuracy of the Walk-and-Turn Test requires a thorough understanding of its administration and potential sources of error. An experienced DUI defense attorney can analyze your specific situation and identify any procedural errors that may have compromised the validity of this field sobriety test.

3. The One-Leg Stand Test

The One-Leg Stand Test is another standardized field sobriety test (SFST) used by law enforcement to assess impairment in drivers suspected of driving under the influence (DUI). This test focuses on the individual's balance and stability, requiring them to stand on one leg while following specific instructions.

Understanding the balance and stability requirements of the One-Leg Stand Test

During the One-Leg Stand Test, the driver is instructed to raise one foot approximately six inches off the ground and maintain balance while counting out loud for a specified duration, typically 30 seconds. The individual is expected to keep their arms at their sides and maintain their balance without swaying, hopping, or putting their foot down.

This test aims to assess the driver's ability to divide attention between physical coordination and mental tasks. Impairment caused by alcohol or drugs can affect an individual's balance and stability, making it difficult for them to successfully complete this test.

Key defense strategies for challenging the One-Leg Stand Test results

There are several defense strategies that can be employed to challenge the validity of One-Leg Stand Test results:

Procedural errors

Just like any other SFST, the One-Leg Stand Test must be administered correctly by law enforcement officers. Any procedural errors or deviations from the established guidelines can compromise the accuracy and reliability of the test results. For example, if the officer fails to provide clear instructions or does not properly demonstrate the test, it can lead to inaccurate interpretations of impairment.

Physical conditions

Certain physical conditions or injuries can impact an individual's ability to perform the One-Leg Stand Test, even if they are not under the influence of alcohol or drugs. Conditions such as inner ear problems, leg injuries, or other medical issues may affect an individual's balance and stability, leading to false indicators of impairment during this test.

Environmental factors

The conditions in which the One-Leg Stand Test is conducted can also affect the results. Uneven surfaces, poor lighting, inclement weather, or other external factors can make it more challenging for an individual to maintain their balance and stability during the test, potentially leading to inaccurate assessments of impairment.

By challenging the administration and interpretation of the One-Leg Stand Test, a skilled DUI defense attorney can raise doubts about the accuracy and reliability of the evidence presented against their client. This underscores the importance of consulting with a knowledgeable attorney who specializes in field sobriety testing issues to build a strong defense strategy.

Other Field Sobriety Tests Used by Law Enforcement

When it comes to assessing a driver's impairment during a DUI stop, law enforcement officers may use a variety of field sobriety tests to gather evidence. While standardized tests like the Horizontal Gaze Nystagmus (HGN), Walk-and-Turn, and One-Leg Stand are commonly recognized, there are other non-standardized tests that can still carry evidentiary weight in DUI cases. These additional tests include:

  1. Modified-Position-of-Attention Test: This test involves observing a suspect's ability to maintain a stance with their heel and toe touching while tilting their head back and estimating 30 seconds.
  2. Romberg Test: The Romberg test evaluates a person's balance and internal clock by requiring them to stand with their feet together, head tilted back, eyes closed, and estimate 30 seconds.
  3. Finger-to-Nose Test: During this test, the individual is asked to close their eyes and touch the tip of their nose with the tip of their index finger, alternating between left and right hands.
  4. Alphabet Test: Suspects may be asked to recite the alphabet backward to assess cognitive impairment.
  5. Finger Count Test: In this test, individuals are instructed to touch the tip of each finger on one hand with their thumb while simultaneously counting up from one to four or five.
  6. Counting Test: A simple test involving counting fingers or numbers forwards or backwards.
  7. Preliminary Alcohol Screening (PAS) Test: This portable breathalyzer test measures a person's blood alcohol concentration (BAC) at the scene.

Navigating the legal complexities of DUI cases requires expert guidance. By consulting a skilled DUI defense attorney, you can ensure that your rights are protected and increase your chances of achieving a favorable outcome in court.

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