DUI Laws
Field Sobriety Tests in California DUI Cases — What They Are and How to Challenge Them
Field sobriety tests are roadside coordination exercises used by officers to build probable cause for a DUI arrest. They are not scientifically infallible — and an experienced attorney can challenge how they were administered and scored.
By Michael P. Kade — Former LAPD Officer & Criminal Defense Attorney · Updated
Educational purposes only — not legal advice. This article provides general information about California DUI law and does not create an attorney-client relationship. Consult a licensed attorney for advice specific to your situation.
Key Takeaways
- —Field sobriety tests are voluntary for drivers 21 and over — you may decline without criminal penalty
- —Only three tests are NHTSA-standardized: HGN, walk-and-turn, and one-leg stand
- —Non-standardized tests like finger-to-nose and Rhomberg balance have no validated accuracy rate
- —Medical conditions, footwear, road surface, and lighting all affect performance
- —Officers must be trained and follow specific protocols — deviations undermine reliability
When an officer pulls you over on suspicion of DUI in California, they will typically ask you to step out of the vehicle and perform a series of roadside exercises called field sobriety tests (FSTs). These tests are designed to give the officer observable clues of impairment to establish probable cause for an arrest. What many drivers do not realize is that FSTs are not mandatory for drivers 21 and over, they are not perfectly accurate even under ideal conditions, and the results can be challenged in court.
The Three NHTSA-Standardized Tests
The National Highway Traffic Safety Administration (NHTSA) has validated only three field sobriety tests as having a statistically meaningful correlation with BAC levels above 0.08%: (1) the Horizontal Gaze Nystagmus (HGN) test, where the officer tracks involuntary eye jerking as you follow a stimulus; (2) the Walk-and-Turn test, a divided-attention exercise requiring you to walk heel-to-toe along a line, turn, and return; and (3) the One-Leg Stand test, where you balance on one foot while counting aloud. Even under controlled conditions, NHTSA's own research shows these tests have error rates — the HGN is approximately 88% accurate, the walk-and-turn approximately 79%, and the one-leg stand approximately 83%.
Non-Standardized Tests
Many California officers also administer non-standardized tests such as the finger-to-nose test, the Rhomberg balance test (estimating 30 seconds with eyes closed), the hand-pat test, and the finger-count test. These tests have no NHTSA-validated accuracy rate and are more susceptible to challenge. Their results are still admissible as observations of the officer, but a skilled attorney can highlight the lack of scientific validation to undermine their weight with a jury.
Factors That Affect Performance
Dozens of factors unrelated to alcohol can cause a sober person to perform poorly on FSTs: inner ear disorders, back or knee injuries, neurological conditions, fatigue, anxiety, age, weight, footwear (particularly heels), uneven road surfaces, passing traffic, bright headlights, and cold weather. Officers are trained to ask about medical conditions before administering the tests, but they do not always do so — and their failure to account for these factors is a significant line of attack.
Are Field Sobriety Tests Mandatory?
In California, drivers 21 and older who are not on DUI probation are generally not required to perform field sobriety tests. Declining will not result in a license suspension (unlike refusing a post-arrest chemical test). However, the officer may still arrest you based on other observations — odor of alcohol, slurred speech, red eyes, or erratic driving. Drivers under 21 or on DUI probation may be subject to different rules, and you should consult an attorney about your specific situation.
Penalties at a Glance
| Offense / Situation | Potential Penalty |
|---|---|
| Declining FSTs (21+ not on probation) | No criminal or DMV penalty |
| Poor FST performance used as probable cause | Supports arrest; admissible at trial |
| FST results combined with BAC evidence | Strengthens prosecution's case significantly |
Penalties shown are general ranges. Actual sentences depend on the specific facts of your case.
How Attorney Kade Defends These Cases
- —Challenge whether the officer was properly trained and certified to administer NHTSA-standardized tests
- —Identify deviations from the NHTSA-required administration protocol
- —Present medical evidence explaining poor performance unrelated to alcohol
- —Attack the lighting, road surface, and environmental conditions at the test location
- —Cross-examine the officer on whether they asked about medical conditions before testing
- —Highlight the inherent error rates of even the standardized tests
- —Use dashcam or bodycam footage to contradict the officer's written observations
Frequently Asked Questions
No. Field sobriety tests (FSTs) are voluntary in California. You are not legally required to perform them, and refusing does not trigger the same automatic penalties as refusing a post-arrest chemical test. However, an officer may still arrest you based on other observations.
The three NHTSA-standardized field sobriety tests are: (1) the Horizontal Gaze Nystagmus (HGN) test, which checks for involuntary eye movement; (2) the Walk-and-Turn test; and (3) the One-Leg Stand test. Only these three have been validated by NHTSA research. Other tests — like reciting the alphabet or counting backwards — are non-standardized and more easily challenged.
Yes. FST results are highly subjective and can be challenged on many grounds: poor lighting, uneven pavement, medical conditions (inner ear disorders, back problems, obesity), improper officer instructions, or failure to follow NHTSA standardized procedures. An experienced DUI attorney will scrutinize the officer's training records and the conditions under which the tests were administered.