It's Not Pass or Fail- nterpretation of Standardized Field Sobriety Tests (SFSTs) in California

In California, Standardized Field Sobriety Tests (SFSTs) play a central role in DUI (Driving Under the Influence) investigations. These tests are designed to help law enforcement officers determine whether a driver is impaired by alcohol or drugs. 
While SFSTs are useful tools, they are not definitive proof of intoxication. Prosecutors typically combine SFST results with chemical test results (breath, blood), the driving pattern, and other officer observations. However, if chemical tests are unavailable or suppressed, SFSTs become a more critical piece of evidence—and are more aggressively scrutinized by the defense.

Overview of SFSTs
The National Highway Traffic Safety Administration (NHTSA) developed a standardized battery of three field sobriety tests in the 1980s. These tests are: (1) Horizontal Gaze Nystagmus (HGN), (2) Walk-and-Turn (WAT), and (3) the One-Leg Stand (OLS).

California law enforcement officers are trained to administer these tests in a consistent and standardized manner to help establish probable cause for a DUI arrest under Vehicle Code § 23152.

Horizontal Gaze Nystagmus (HGN)
Nystagmus is the involuntary jerking of the eyes, which becomes more pronounced when a person is under the influence of alcohol or certain drugs. In the HGN test, the officer observes the driver’s eye movement as they follow a slowly moving object (usually a pen or finger) from side to side.

Indicators of impairment include: Lack of smooth pursuit, Distinct nystagmus at maximum deviation, and the Onset of nystagmus before 45 degrees

Each eye is scored separately, for a total of six possible clues. According to NHTSA, the presence of four or more clues suggests a BAC of 0.08% or higher.

The limitations of the test typically revolve around the fact that HGN can be affected by medical conditions, fatigue, or medications, and it is a technical test requiring proper training in the administration and interpretation.

Walk-and-Turn (WAT)
The WAT is a divided attention test, requiring both mental focus and physical coordination. The driver is instructed to take nine heel-to-toe steps, turn on one foot, and return nine steps.

Clues of impairment include:

• Inability to keep balance during instructions
• Starting too soon
• Stepping off the line
• Incorrect number of steps
• Using arms for balance
• Improper turn

The limitations of the test are typically considered by defense attorneys where conditions such as uneven surfaces, poor footwear, injuries, age, or obesity can affect performance, or the ervousness or misunderstanding instructions by the driver can lead to poor results.

One-Leg Stand (OLS)
In the OLS test, the driver is asked to stand on one foot while counting aloud for 30 seconds. The officer watches for:

• Swaying while balancing
• Using arms for balance
• Hopping
• Putting the foot down

Two or more clues suggest possible impairment.

Limitations:

• Similar to WAT, balance issues due to age, injury, or footwear can affect performance.
• Not everyone has equal balance, even sober.
• Uneven or sloped terrain may cause inaccurate assessments.

Legal and Scientific Considerations in California

A. Standardization and ReliabilityFor SFST results to be admissible and credible in California DUI cases, the tests must be administered in accordance with NHTSA guidelines, officers must be properly trained and certified, and environmental conditions (weather, lighting, surface) must be considered. Failure to follow standardized procedures can lead to suppression of SFST evidence.

B. Subjectivity and Officer BiasDespite the standardization efforts, interpretation remains highly subjective:

• Officers must judge subtle cues, like how much a person sways or whether steps are “heel-to-toe.”
• Personal bias, lack of training, or confirmation bias (expecting impairment) can influence scoring.
• Dashcam or bodycam footage may be used to challenge the officer’s observations in court.

Role in Establishing Probable Cause
In California, SFSTs are primarily used to establish probable cause for a DUI arrest and to justify further testing (like breath or blood tests). They are often performed after initial signs of impairment such as: erratic driving, and odor of alcohol coming from the driver, and the driver having slurred speech or red eyes

Admissibility and Challenges in Court
A. Cross-Examination and Expert WitnessesDefense attorneys often challenge SFST results by:

• Questioning the officer’s training or credibility
• Highlighting physical or medical conditions affecting performance
• Using expert testimony to dispute the accuracy of SFSTs

An expert in forensic toxicology or DUI procedures may explain to a jury that SFSTs are not scientifically conclusive, and many sober people could fail them under stress.

B. Jury InterpretationJurors may be persuaded by an officer's confident testimony, but video evidence can sometimes paint a different picture. Defense attorneys may argue that:

• The defendant was cooperative and responsive.
• The test conditions were unfair or poorly explained.
• The performance did not show clear signs of impairment.

Non-Standardized Field Sobriety Tests
Officers sometimes use non-standardized tests, such as:

• Reciting the alphabet
• Counting backward
• Touching nose with eyes closed

These are not recognized by NHTSA and are more vulnerable to legal challenge as they lack uniform scoring and have no scientific validation.


In short, in California, Standardized Field Sobriety Tests are a key part of DUI investigations, offering officers a structured way to assess impairment. However, their subjective nature, sensitivity to external factors, and reliance on proper training make them vulnerable to challenge. Courts generally allow SFST evidence, but its interpretive value depends heavilyon how well the tests were conducted, the specific circumstances, and the credibility of the officer involved.

Defendants charged with a DUI should always consult experienced legal counsel, as there are numerous viable defenses rooted in procedural error, physical limitations, or scientific dispute. Ultimately, while SFSTs may help build a case for DUI, they are not infallible, and their results should always be examined in context.

If you've recieved a DUI, and wish to contact Devina, you can do so here.