When you’re pulled over for suspected drunk driving, law enforcement may ask you to perform field sobriety tests—a series of physical tasks designed to detect signs of impairment. These roadside tests have become a standard part of DUI investigations, but one question remains: Are field sobriety tests always accurate?
In this post, we’ll examine the reliability of these tests, what factors influence their accuracy, and how they impact DUI cases.
What Are Field Sobriety Tests?
Field Sobriety Tests (FSTs) are standardized assessments used by police officers during DUI stops to help determine whether a driver is impaired by alcohol or drugs. The most commonly used tests are part of the Standardized Field Sobriety Test (SFST) battery developed by the National Highway Traffic Safety Administration (NHTSA), which includes:
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Horizontal Gaze Nystagmus (HGN) – Observing eye movement as the subject follows a moving object.
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Walk-and-Turn (WAT) – Walking heel-to-toe in a straight line, then turning and returning.
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One-Leg Stand (OLS) – Standing on one foot for 30 seconds.
These tests are designed to evaluate balance, coordination, attention, and the ability to follow instructions—skills that alcohol and drugs can impair.
How Accurate Are Field Sobriety Tests?
According to NHTSA studies:
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HGN test accuracy: ~77%
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Walk-and-Turn test accuracy: ~68%
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One-Leg Stand test accuracy: ~65%
When all three are used together, their combined accuracy rate is estimated around 91% in ideal conditions.
However, these numbers are based on controlled conditions with trained officers. In real-world scenarios, the accuracy can be significantly lower due to several factors.
Factors That Affect Accuracy
1. Officer Training and Administration
Proper administration is key to accuracy. If an officer improperly instructs or evaluates the test, it can lead to false positives. Not all officers follow exact procedures, which can reduce the test’s reliability.
2. Road and Environmental Conditions
Uneven pavement, poor lighting, weather (rain, snow, wind), and passing traffic can impact a person’s ability to perform the tests—even if they are sober.
3. Medical Conditions
Individuals with medical issues such as inner ear problems, neurological disorders, leg injuries, or even anxiety may struggle with balance-based tasks. Age and weight can also affect performance.
4. Clothing and Footwear
Heels, boots, or loose-fitting shoes can impair a person’s ability to walk heel-to-toe or balance on one leg. This can lead to incorrect assessments.
5. Language and Comprehension Barriers
Non-native speakers or people with learning disabilities may misinterpret the instructions, affecting their performance. This isn’t necessarily a sign of intoxication but may still be used as evidence.
Are Field Sobriety Tests Mandatory?
In most states, you are not legally required to take field sobriety tests. Refusing them cannot result in automatic license suspension (unlike refusing a chemical breath test under implied consent laws). However, refusal may still raise suspicion and lead to arrest.
Knowing your rights is essential. You can politely decline to participate and request to speak with an attorney.
Can You Challenge Field Sobriety Tests in Court?
Yes. An experienced DUI defense attorney can challenge the validity of field sobriety tests in several ways:
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Questioning the officer’s training and test administration
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Highlighting environmental and physical factors affecting performance
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Showing that the tests are subjective and prone to bias
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Citing medical or psychological reasons for poor performance
Many DUI cases are successfully contested based on flawed or improperly administered FSTs.
Are There Better Alternatives?
While field sobriety tests are widely used, chemical testing (breath, blood, or urine) is more scientifically reliable in determining blood alcohol concentration (BAC).
However, even chemical tests can be challenged if they are:
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Administered incorrectly
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Based on faulty equipment
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Delayed beyond the time of the stop
For law enforcement, FSTs are typically used as preliminary tools to establish probable cause for arrest or further testing.
The Role of Field Sobriety Tests in DUI Arrests
Although not mandatory, field sobriety tests can be used as evidence in court to support DUI charges. However, they are not foolproof, and their subjective nature means they must be interpreted with caution.
Many legal professionals argue that the tests are biased toward failure, especially under stress or unusual conditions. Courts may still consider them, but they are rarely the only factor in securing a conviction.
Conclusion
Field sobriety tests are a common tool in DUI stops, but they’re far from perfect. While designed to detect impairment, their accuracy is influenced by human error, environmental conditions, and individual circumstances. If you’ve been arrested based on a failed field sobriety test, don’t assume it’s an open-and-shut case.
Understanding your rights, the limitations of these tests, and how they are used in court can help you make informed decisions—and if necessary, mount a strong legal defense.
