Field sobriety tests (FSTs) are a series of physical and cognitive tasks used by law enforcement to assess whether a driver is under the influence of alcohol or drugs.
These standardized tests include the horizontal gaze nystagmus (HGN) test, the walk-and-turn test, and the one-leg stand test.
Officers observe a driver’s balance, coordination, and ability to follow instructions to determine impairment. While officers are trained to administer these tests according to standardized guidelines, factors that can affect the reliability of FSTs include the individual’s ability to follow instructions, medical conditions, and the officer’s subjective interpretation of the results.
These tests are not always a fair and accurate measure of impairment and can be challenged in court.
At Arja Shah Law, we understand the potential issues with these tests and can help build a strong defense if you believe a medical condition that might have influenced your performance on a field sobriety test. Contact us today for a consultation and to learn how we can help protect your rights.
This article will cover the following subtopics:
- How Law Enforcement Administers Field Sobriety Tests
- Are Field Sobriety Tests Reliable?
- What are Factors that Can Impact Performance in a Field of Sobriety Test
- Medical Conditions that Can Affect Field Sobriety Testing
- What Defenses Can Be Used Against a FST
- Contact DUI Defense Attorney Arja Shah
How Law Enforcement Administers Field Sobriety Tests
Law enforcement officers rely on standardized field sobriety tests (FSTs) to determine if a driver is impaired by alcohol or drugs. These tests are designed to evaluate physical coordination and cognitive abilities, but it’s important to remember that factors beyond intoxication can affect the results of these tests.
The three most commonly administered tests include the walk-and-turn test, the one-leg stand, and the horizontal gaze nystagmus (HGN) test. Below, we explain how these tests are performed and what factors could potentially affect their accuracy.
① The Horizontal Gaze Nystagmus (HGN) Test
The HGN test is typically the first test an officer administers. It involves tracking a moving object, such as a pen or a finger, to observe the eye’s involuntary jerking movements, which are often exaggerated by alcohol impairment. Officers are trained to detect this jerking as a sign of intoxication, but neurological conditions or certain medications can cause similar symptoms, leading to false positives.
② The Walk-and-Turn Test
The walk-and-turn test is a divided attention task where the driver is instructed to take a series of steps in a straight line, turn on one foot, and return in the same manner. This test evaluates balance, coordination, and the ability to follow instructions. However, health conditions like arthritis, leg injuries, or even certain medications can make it difficult to complete this test, causing the officer to believe that alcohol impairment is the issue. Environmental factors, such as uneven ground, may also affect your performance on this test.
③ The One-Leg Stand Test
In the one-leg stand test, drivers are instructed to stand on one leg while counting aloud for 30 seconds. This test challenges a person’s balance and ability to concentrate on both a physical task and cognitive tasks simultaneously. Medical conditions that affect balance, such as vertigo or muscle disorders, can lead to misinterpreted signs of intoxication.
Are Field Sobriety Tests Reliable?
Field sobriety tests (FSTs) are often relied upon by law enforcement to assess a driver’s impairment. However, their reliability is widely debated due to subjective interpretation and the potential for external factors to impact performance. Below, we explore how reliable FSTs really are and the factors that can undermine their accuracy.
▶ Field Sobriety Test Accuracy Rates
Studies have shown that the three standardized FSTs—the horizontal gaze nystagmus (HGN), the walk-and-turn, and the one-leg stand—vary in accuracy. According to a study by the National Highway Traffic Safety Administration (NHTSA), these tests have the following accuracy rates when performed under ideal conditions:
- Horizontal Gaze Nystagmus (HGN): 77% accurate in predicting blood alcohol concentration (BAC) levels of 0.08 or higher.
- Walk-and-Turn: 68% accurate in predicting BAC levels of 0.08 or higher.
- One-Leg Stand: 65% accurate in predicting BAC levels of 0.08 or higher .
These percentages show that while FSTs can be useful, they are far from foolproof and leave room for error, especially in real-world scenarios where conditions are not ideal.
▶Legal Scrutiny of Field Sobriety Tests
Due to their inherent flaws, field sobriety tests have been challenged in court on numerous occasions. For instance, the subjective nature of these tests can lead to wrongful DUI arrests, particularly in cases where other factors influenced the results.
Furthermore, Arizona courts do not always consider FST results as conclusive evidence of impairment; they are often just one part of the broader investigation .
What are Factors that Can Impact Performance in a Field of Sobriety Test
Field sobriety tests are designed to assess physical coordination and cognitive ability, but several external factors and medical conditions can interfere with accurate results.
⑴ Nervousness
Anxiety and stress are common reactions to being pulled over by law enforcement. This heightened emotional state can cause shaking, poor balance, or unsteady movements, making it difficult for even a sober individual to perform well on field sobriety tests.
⑵ Road and Weather Conditions
The environment where the test is conducted can significantly impact performance. Uneven surfaces, gravel, rain, or poor lighting may affect a person’s ability to walk heel-to-toe or maintain balance during other tests.
⑶ Footwear
Wearing inappropriate shoes, such as high heels, boots, or sandals, can make it challenging to maintain proper posture and balance. Footwear can unfairly contribute to failing the walk-and-turn or one-leg stand tests.
⑷ Age or Weight
Age and body composition can influence physical balance and coordination. Older adults and individuals with higher BMIs may naturally have difficulty with tasks that require precise movements or balance, which can result in false indications of impairment.
⑸ Medical Conditions
Certain medical conditions may directly impact a person’s ability to perform well on field sobriety tests. These conditions include, but are not limited to, vertigo, arthritis, neurological disorders, and diabetes. Each of these health issues can create symptoms that mimic impairment, leading to inaccurate results.
Medical Conditions that Can Affect Field Sobriety Testing
Certain medical conditions can drastically affect an individual’s ability to complete an FST. Some common conditions that may influence test performance include:
- Vertigo and Inner Ear Issues: These conditions can cause dizziness, leading to balance problems.
- Arthritis and Joint Problems: Individuals with arthritis may have difficulty performing tasks requiring mobility, such as walking heel-to-toe or standing on one leg.
- Neurological Disorders: Conditions such as Parkinson’s disease, multiple sclerosis, or brain injuries can result in poor coordination, which may resemble the effects of intoxication.
- Diabetes: Low blood sugar levels (hypoglycemia) can cause symptoms like confusion, dizziness, or shaking, all of which could lead to failing a sobriety test.
- Vision Impairments: The horizontal gaze nystagmus test relies heavily on a person’s ability to focus on a moving object, which may be difficult for individuals with certain eye conditions.
These health concerns must be considered, as they can serve as a valid explanation for failing a field sobriety test despite being sober.
What Defenses Can Be Used Against a FST
Arizona law (ARS §28-1381) allows for DUI charges to be challenged based on unreliable field sobriety test results, especially if medical conditions or other factors hindered performance.
Common defenses include:
- Challenging the Test Conditions: A skilled defense attorney can argue that environmental factors, such as uneven ground or poor lighting, contributed to the failure.
- Medical Documentation: Providing medical records that verify a client’s condition can demonstrate that the poor performance was due to health issues rather than intoxication.
- Inaccuracy of the FST: Field sobriety tests are not foolproof and can be influenced by a variety of non-alcohol-related factors. An experienced DUI attorney can argue that these tests should not be the sole basis for a DUI conviction.
Attorney Arja Shah’s extensive experience with vehicular crimes, including DUI defense, enables her to assess the validity of FST results and build a strong defense.
Contact DUI Defense Attorney Arja Shah
With over 3,000 successful defenses under her belt and extensive experience in Arizona courts, Ms. Shah can evaluate your case, challenge the results of the field sobriety tests, and fight for the best possible outcome.
Contact Arja Shah Law today at (602) 560-7408 for a free consultation and personalized defense strategy.
