Field Sobriety Test

Interactive Guide to NHTSA Standardized Testing

⚠️ Important Disclaimer

This is an educational tool only. It is NOT a substitute for professional medical or legal assessment. Never drive if you have consumed alcohol or are impaired in any way.

What Are Field Sobriety Tests?

Field sobriety tests are procedures used by law enforcement to assess whether a driver is impaired due to alcohol or drug consumption. These tests are part of the Standardized Field Sobriety Testing (SFST) system developed by the National Highway Traffic Safety Administration (NHTSA).

The Three Standardized Field Sobriety Tests

1. Horizontal Gaze Nystagmus (HGN)

Observes involuntary eye movements

88% accurate at ≥ 0.08% BAC

2. Walk-and-Turn (WAT)

Tests balance and coordination

79% accurate at ≥ 0.08% BAC

3. One-Leg Stand (OLS)

Tests balance and concentration

83% accurate at ≥ 0.08% BAC

Combined Accuracy: According to the 1998 San Diego validation study, when all three tests are administered together, they have extremely high reliability (91%) in detecting drivers with a blood alcohol concentration (BAC) of 0.08% or higher.

Test Limitations

Several factors can affect test performance, even in sober individuals:

  • Medical conditions or disabilities
  • Age and physical fitness level
  • Medications or fatigue
  • Environmental factors (uneven surfaces, poor lighting, weather)
  • Nervousness or anxiety

Frequently Asked Questions

The HGN test checks for an involuntary jerking of the eye (nystagmus) as it gazes to the side. While some nystagmus is natural, alcohol exaggerates this effect, causing the eye to jerk noticeably at smaller angles (prior to 45 degrees). Officers look for three specific clues in each eye: lack of smooth pursuit, distinct nystagmus at maximum deviation, and onset of nystagmus prior to 45 degrees.

The Walk-and-Turn is a "divided attention" test that requires you to listen to instructions while maintaining balance. You must take nine heel-to-toe steps along a straight line, turn on one foot, and take nine steps back. Officers look for eight indicators of impairment, such as stepping off the line, using arms for balance, or starting too soon.

The One-Leg Stand tests balance and concentration. You are asked to stand with one foot approximately six inches off the ground and count aloud by thousands (e.g., "one thousand one") for 30 seconds. Indicators of impairment include swaying, hopping, using arms for balance, or putting the foot down.

No field sobriety test is 100% accurate. According to NHTSA's 1998 San Diego validation study, the tests have the following accuracy rates for detecting a BAC of 0.08% or higher: HGN (88%), Walk-and-Turn (79%), and One-Leg Stand (83%). However, medical conditions, age, weight, and environmental factors can all produce false positives.

Before You Begin

Safety Requirements

  • Ensure you are in a safe, controlled environment
  • Use a flat, even surface
  • Ensure adequate lighting
  • Have a friend nearby if attempting balance tests
  • Stop immediately if you feel unsafe

How This Works

You will perform each of the three standardized field sobriety tests and report your observations. The system will evaluate your responses based on NHTSA criteria.

Remember: This is for educational purposes only. The results are not scientifically valid or legally admissible.

Do you have any conditions that might affect your performance?

Medical conditions, injuries, or physical limitations may affect test results. If so, keep this in mind when interpreting your results.

Test 1 of 3

Horizontal Gaze Nystagmus (HGN) Test

What This Tests

Horizontal gaze nystagmus is an involuntary jerking of the eyeball that occurs naturally when the eyes rotate at high peripheral angles. When a person is intoxicated, this jerking becomes more exaggerated and occurs at lesser angles.

Instructions

  1. Hold a pen, pencil, or your finger about 12-15 inches from your face
  2. Keep your head still and follow the object with your eyes only
  3. Move the object slowly from center to your far right
  4. Then move it slowly from center to your far left
  5. Observe your eye movements carefully
  6. Repeat 2-3 times for each eye

Watch How to Do the Horizontal Gaze Nystagmus Test

What to Look For

Officers observe the following indicators (clues) during this test:

Left Eye Observations:

Right Eye Observations:

Evaluation Criteria: According to the 1998 San Diego Study, if 4 or more clues are present, there is an 88% likelihood of BAC ≥ 0.08%.

Test 2 of 3

Walk-and-Turn (WAT) Test

What This Tests

This is a divided attention test that assesses your ability to follow instructions while performing physical movements requiring balance and coordination.

Instructions

  1. Stand with your feet heel-to-toe on an actual or imaginary straight line
  2. Keep your arms at your sides
  3. Listen to all instructions before beginning
  4. When told to start, take 9 heel-to-toe steps along the line
  5. Count each step out loud ("one, two, three...")
  6. When you reach the 9th step, turn around on one foot using small steps
  7. Take 9 heel-to-toe steps back along the line
  8. Keep watching your feet and keep your arms at your sides

Watch How to Do the Walk-and-Turn Test

Safety First: Only perform this test in a safe area where you won't fall or injure yourself. Have someone nearby if possible.

Perform the test, then check any indicators you observed:

Evaluation Criteria: According to the 1998 San Diego Study, if 2 or more indicators are present, there is a 79% likelihood of BAC ≥ 0.08%.

Test 3 of 3

One-Leg Stand (OLS) Test

What This Tests

This test evaluates your balance and concentration by requiring you to maintain a physical position while counting aloud.

Instructions

  1. Stand with your feet together and arms at your sides
  2. When instructed, raise one leg (either leg) approximately 6 inches off the ground
  3. Keep your foot pointed straight forward and parallel to the ground
  4. Keep your eyes on your raised foot
  5. Count aloud: "one thousand one, one thousand two, one thousand three..." until told to stop
  6. Continue for 30 seconds (until "one thousand thirty")

Watch How to Do the One-Leg Stand Test

Safety First: Perform this test near a wall or sturdy object you can grab if needed. Stop immediately if you feel unsafe.

30-Second Timer

30

Perform the test, then check any indicators you observed:

Evaluation Criteria: According to the 1998 San Diego Study, if 2 or more indicators are present, there is an 83% likelihood of BAC ≥ 0.08%.

Test Results & Interpretation

Understanding Your Results

These results are based on NHTSA standardized field sobriety test criteria used by law enforcement. However, remember that:

  • This is an educational tool, not a diagnostic test
  • Many factors can affect test performance beyond alcohol consumption
  • Self-reporting may not be as accurate as trained officer observation
  • The tests are designed to detect BAC levels, not actual impairment from all sources

Important Reminders

Never drive if you have consumed alcohol or are impaired in any way, regardless of these test results.

If you are experiencing actual impairment or have concerns about substance use, please consult with a healthcare professional or contact local emergency services.

About Field Sobriety Tests

Test Accuracy (1998 San Diego Study)

Research by the NHTSA (Validation of the Standardized Field Sobriety Test Battery at BACs Below 0.10 Percent, 1998) has shown that when properly administered by trained officers, the tests are highly accurate at detecting BAC ≥ 0.08%:

  • HGN Test: 88% accurate
  • Walk-and-Turn: 79% accurate
  • One-Leg Stand: 83% accurate
  • All three combined: 91% accurate

Limitations

Field sobriety tests can produce false positives due to:

  • Medical conditions (inner ear problems, neurological conditions, eye disorders)
  • Physical limitations (age, weight, injuries, disabilities)
  • Medications that affect balance or coordination
  • Environmental factors (uneven surfaces, poor lighting, weather conditions)
  • Nervousness, fatigue, or stress

Legal Context

Field sobriety tests serve to establish probable cause for arrest and provide evidence in legal proceedings. They are often followed by chemical tests (breath, blood, or urine) to determine actual BAC levels. In most jurisdictions, a BAC of 0.08% or higher is the legal limit for driving.