When an officer asks you to step out of your vehicle and perform field sobriety tests, most people have no idea what is actually being evaluated. They assume the officer will know if they "pass" or "fail" based on obvious stumbling or falling. The reality is far more precise — and far more easy to fail even when sober.
Field sobriety tests are standardized by the National Highway Traffic Safety Administration (NHTSA). There are three tests that meet NHTSA's standards, and officers are trained to look for very specific clues on each one. Understanding what those clues are — and why completely sober people regularly exhibit them — is essential information.
Test 1: Horizontal Gaze Nystagmus (HGN)
What the officer does
The officer holds a pen or finger approximately 12-15 inches from your face and moves it slowly from side to side while watching your eyes. They are looking for involuntary jerking of the eyeball as it tracks the object.
What they're scoring
Officers look for 6 total clues — 3 per eye:
- Lack of smooth pursuit (eye jerks instead of tracking smoothly)
- Distinct nystagmus at maximum deviation (eye jerks when held at the far edge)
- Onset of nystagmus prior to 45 degrees (jerking begins before the eye reaches the corner)
4 or more clues out of 6 is considered an indicator of impairment under NHTSA guidelines.
Why sober people fail this test
Nystagmus — the involuntary eye jerking HGN measures — can be caused by dozens of conditions and medications completely unrelated to alcohol. These include: inner ear disorders, certain prescription medications (including some antihistamines and anti-seizure drugs), traumatic brain injury, caffeine, nicotine, and even extreme fatigue. Additionally, officers must be trained precisely in pen distance and speed. If the pen is too close, too far, or moved too quickly, the test produces unreliable results.
Test 2: Walk-and-Turn (WAT)
What the officer does
The officer instructs you to walk nine steps heel-to-toe along a real or imaginary line, turn on one foot, and walk back nine steps the same way. They observe from the instruction phase onward.
What they're scoring — 8 possible clues:
- Cannot keep balance during instructions
- Starts before instructions are finished
- Stops while walking
- Does not touch heel-to-toe (gap of more than half an inch)
- Steps off the line
- Uses arms for balance (raises arms more than 6 inches)
- Loses balance or falls during the turn
- Takes wrong number of steps
2 or more clues is considered an indicator of impairment.
Why sober people fail this test
The walk-and-turn is performed on the side of a road at night, often on uneven pavement, with cars passing and flashing lights. The "line" is frequently imaginary. People over 65, those with inner ear problems, back injuries, leg injuries, or anyone more than 50 pounds overweight will struggle with this test under any conditions. High heels or dress shoes add another failure factor. Nervousness — which virtually everyone experiences when pulled over by police — causes many of the scored clues to appear in completely sober people.
Test 3: One-Leg Stand (OLS)
What the officer does
The officer instructs you to stand with one foot approximately 6 inches off the ground and count out loud by thousands (one-thousand-one, one-thousand-two) for 30 seconds while keeping your eyes on your raised foot.
What they're scoring — 4 possible clues:
- Swaying while balancing
- Using arms for balance (raises arms more than 6 inches)
- Hopping
- Puts foot down
2 or more clues is considered an indicator of impairment.
Why sober people fail this test
Standing on one leg for 30 seconds while counting, in dress shoes, on the shoulder of a highway, at night, with a police officer watching — this is not a normal human activity under any circumstances. Research has shown that individuals over 65, those with certain leg or back conditions, and people with inner ear issues consistently perform poorly regardless of alcohol consumption. The sway threshold (arms raised more than 6 inches) is extremely sensitive.
Non-Standardized Tests: Be Especially Careful
Beyond the three NHTSA-standardized tests above, officers sometimes ask you to perform other tests: touching your finger to your nose, reciting the alphabet (often backwards), counting backwards, or standing with your feet together and tilting your head back with eyes closed.
These tests have no scientific validation for DWI detection under NHTSA standards. Despite this, officers observe and document performance on them, and prosecutors present that documentation at trial. The absence of scientific backing doesn't prevent their use — it just provides your attorney with another angle of attack.
Can You Refuse Field Sobriety Tests?
In most states, yes — field sobriety tests are voluntary. Unlike the evidentiary breath test at the station, refusing field sobriety tests typically does not trigger automatic license suspension under implied consent laws. The officer may tell you refusal looks bad, but the legal consequences of refusal are usually limited to the officer noting the refusal in their report.
Whether refusing is the right call depends heavily on your specific situation and state. That is a conversation worth having with a DWI attorney before you ever need it.
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