How Reliable Are Standardized Field Sobriety Tests by Law Enforcement?

In North Carolina, law enforcement officers use three standardized field sobriety tests (SFSTs) to determine if a driver is impaired by alcohol. These tests include the horizontal gaze nystagmus (HGN) test, the walk-and-turn test, and the one-leg stand test. Officers look for clues that indicate intoxication, like swaying, stumbling or difficulty following instructions.

While controversial, SFSTs and officer observations provide evidence for DWI charges in North Carolina when combined with other signs of impairment. Read on to find out more about these tests and how an experienced Asheville DUI attorney can help.

Horizontal Gaze Nystagmus (HGN) Test

One of the most common field sobriety tests is the horizontal gaze nystagmus or HGN test. This test examines involuntary jerking of the eyes as they gaze to the side. When under the influence of alcohol, the eyes will jerk noticeably as they move side to side. Officers will have you follow an object like a pen with just your eyes without moving your head.

Walk-and-Turn Test

The walk-and-turn test requires you to walk heel-to-toe in a straight line, turn in a prescribed manner, and return walking heel-to-toe. It tests balance, coordination, and the ability to follow instructions. Failure to walk in a straight line, missing heel-to-toe contact, using arms for balance, improper turning, or stopping are potential indicators of impairment.

One-Leg Stand Test

The one-leg stand test is exactly what it sounds like. You are instructed to stand on one leg, holding the other foot off the ground, and count out loud for 30 seconds. This test also examines balance, coordination and the ability to follow directions. Swaying, hopping, putting the raised foot down, or using arms for balance can be signs of intoxication.

Reliability Concerns With Standardized Field Sobriety Tests

Standardized field sobriety tests are often relied upon by North Carolina law enforcement officers as evidence of impairment for driving under the influence arrests and charges. However, some concerns have been raised about how reliably these tests measure impairment.

sobriety tests are not reliable in indicating impairment

Accuracy and Subjectivity

The accuracy of SFSTs can be questionable, with some research showing error rates as high as 35% for the Horizontal Gaze Nystagmus test. Officers also have a fair amount of subjectivity and discretion in scoring and interpreting the tests, which can lead to inconsistent results.

Limited Scope

SFSTs only measure certain aspects of impairment, such as balance, coordination and gaze. However, they do not directly measure other important indicators like reaction times, information processing or judgment. Just because someone shows impairment on the SFSTs does not necessarily mean they are too impaired to drive safely.


There is a lot of variability in how officers conduct and score the SFSTs. While officers do receive training, there are many opportunities for differences in administration, scoring, and interpretation. Things like the surface the tests are done on, lighting conditions, temperature, traffic noise, and other environmental factors can also vary and impact the results.

Alternatives to Standardized Field Sobriety Tests

While law enforcement officers typically prefer SFSTs like the walk-and-turn test or one-leg stand test, there are other options you can request. You might ask the officer if you can do a portable breath test using a handheld breathalyzer, which can provide an instant blood alcohol concentration (BAC) reading to determine if you’re over the legal limit of 0.08%.

Some people argue breathalyzers can be inaccurate, but they may still be preferable to difficult coordination tests, especially for those with mobility or balance issues. Another choice is a blood test, where a sample of your blood is drawn and analyzed to get an exact BAC reading. Blood tests are considered very accurate but do require traveling to a medical facility and having blood drawn by a technician.

Get in Touch With an Asheville DUI Attorney Right Away

Many factors can influence a driver’s performance on field sobriety tests, including age, physical conditions, and level of intoxication. The tests themselves have also received criticism regarding their accuracy and reliability. Our firm defends clients against DWI charges and works to call into question the validity of field sobriety test results.

Do you have additional questions about field sobriety tests or DWI charges in NC? Call our office at 828-759-5556 to speak with one of our Asheville DUI Guy attorneys. We offer free initial consultations and will review the details of your case to determine the best defense strategies based on the specifics of your situation. Don’t go through this process alone – we are here to support you every step of the way.

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