California Field Sobriety Tests

Field Tests Are Less Reliable Than Chemical Tests

The best indicator of possible driving impairment is a reliable blood alcohol test. Chemical tests can objectively and accurately determine the driver’s blood alcohol concentration (BAC) within the testing method’s and instrument’s margin of error. Based on this analysis, an opinion on driving impairment can be given using scientific studies.

Field sobriety tests — also called non-chemical tests — are less reliable and often are a poor indicator of driving impairment or sobriety. One reason is the inherent error in subjective evaluations of an individual whose normal performance is unknown.

Nevertheless, field sobriety tests are still used by law enforcement as a tool to:

• Enable an officer to develop probable cause for the stop or arrest
• Assist in establishing possible physical or mental impairment at a time close to driving
• Establish the general causal relationship between alcohol and driving behavior

Understanding the limits of these tests — and why they are used despite those limits — is essential to building a strong DUI defense.

The Legal Framework for DUI Testing in California

In California, the legal limit for blood alcohol content (BAC) is:

• 0.08% for drivers 21 and over
• 0.01% for drivers under 21
• 0.04% for commercial drivers

California also implements an implied consent law. By driving a vehicle on California roads, you consent to chemical testing to determine your BAC if an officer has lawful grounds to request it. Refusal to submit to required tests — including a preliminary alcohol screening test — can lead to serious penalties, including license suspension and fines, independent of whether you are convicted of DUI.

Types of Field Sobriety Tests

A wide variety of field sobriety tests have been used by law enforcement. These include:

• Asking distracting or interrupting questions
• Finger to nose
• Finger count test
• Reciting or writing the alphabet, with signature and time and date
• Counting backwards from 100
• Tracing (a paper-and-pencil exercise)
• Romberg balance test
• Romberg balance test combined with finger to nose
• Nystagmus (HGN)
• One leg stand
• Line walk
• Hand pat
• Picking up coins
• Recitation of date and time
• Standing heel to toe

In actual practice, police officers regularly administer a battery of tests that includes exercises that have not been scientifically validated.

Standardized vs. Non-Standardized Tests

The United States Department of Transportation’s National Highway Traffic Safety Administration (NHTSA) studied several field sobriety tests beginning in 1975, with results published in 1977. Three tests were determined to have a good correlation with impairment — but only when used together and administered in strict compliance with specific testing protocols. These three tests became known as the Standardized Field Sobriety Tests (SFSTs):

• Horizontal gaze nystagmus (HGN)
• Walk and turn
• One leg stand

Any deviation from the required protocols weakens the validity of results from even these three validated tests. All other field sobriety tests officers may use in the field have not been validated by NHTSA research.

Not All Tests Have Been Studied

While there is considerable data on the HGN test and the Romberg test — both of which have clinical origins — many field exercises that officers routinely use have never been studied for reliability or validated as meaningful indicators of alcohol impairment. Some tests are used without any scientific study to support their use. Some merely look for changes in divided attention ability, without any established correlation to a particular BAC level or degree of impairment.

This lack of scientific validation is one of the most powerful arguments a defense attorney can make when challenging field sobriety test evidence in court.

How the Three Standardized Field Sobriety Tests Work

Understanding exactly what officers are looking for during each standardized test helps your attorney identify where the officer’s observations may be flawed, subjective, or affected by factors unrelated to alcohol.

Horizontal Gaze Nystagmus (HGN) Test

The HGN test assesses the involuntary jerking of the eye as it moves side to side. Under the influence of alcohol, nystagmus is exaggerated and occurs at lesser angles. Officers look for three specific indicators of impairment in each eye:

• Lack of smooth pursuit as the eye follows a moving object
• Distinct nystagmus at maximum deviation (when the eye is held at the far edge of its range)
• The onset of nystagmus prior to 45 degrees of deviation

The premise is that people under the influence of alcohol may have difficulty controlling their eye movements. However, as discussed elsewhere on this page, many medical conditions, medications, and neurological factors can produce nystagmus entirely unrelated to alcohol consumption.

Walk-and-Turn (WAT) Test

During the WAT test, the driver is instructed to take nine steps heel-to-toe along a straight line, pivot on one foot, and return in the same manner. Officers look for eight specific indicators of impairment, including:

• Inability to balance during instructions
• Starting before instructions are finished
• Stopping while walking
• Failing to touch heel-to-toe
• Stepping off the line
• Using arms to balance
• An improper turn
• An incorrect number of steps

The test must be administered on a reasonably dry, hard, level, and non-slippery surface — conditions that are rarely perfectly met at a roadside stop.

One-Leg Stand (OLS) Test

In the OLS test, the driver must stand with one foot approximately six inches above the ground and count aloud for 30 seconds. Officers look for four specific indicators of impairment:

• Swaying while balancing
• Using arms to balance
• Hopping to maintain balance
• Putting the foot down before 30 seconds

Age, weight, physical condition, footwear, and uneven surfaces all affect performance on this test independently of alcohol consumption — factors your attorney can use to challenge the officer’s conclusions.

Non-Standardized Field Sobriety Tests: What They Are and Why They’re Unreliable

While the three NHTSA-validated tests are the most commonly challenged, officers regularly administer a range of other non-standardized tests that lack scientific validation. Understanding what each test requires — and where each one fails scientifically — helps your attorney build a targeted challenge.

Finger to Nose Test

The finger to nose test is administered in a variety of formats. Generally, it requires the subject to close their eyes and then touch the tip of their nose with the tip of their index finger, alternating hands.

Importantly, the NHTSA research project found that the finger to nose test — along with the Romberg test — only reflects the presence of alcohol and does not increase the predictive ability of testing. In other words, it cannot meaningfully distinguish between someone who is impaired and someone who simply has alcohol in their system.

Alphabet, Count Down, and Finger Count Tests

The alphabet test requires the subject to recite part of the alphabet — for example, starting at a letter other than A and stopping before Z — or to recite or write the entire alphabet. Contrary to common belief, the test does not require the subject to recite the alphabet backwards.

The count down test requires the subject to count aloud in reverse — for example, from 90 to 70. Sometimes the officer will have the subject stand heel-to-toe while performing the alphabet or count down test, adding a balance component not part of the original task.

The finger count test requires the subject to touch the tip of the thumb to the tip of each finger on the same hand in a specific order while counting — for example, “one, two, three, four — four, three, two, one.” None of these tests have been validated by NHTSA research as reliable indicators of BAC or impairment.

Handwriting Test

Research on handwriting as a sobriety indicator has produced conflicting and ultimately unsupportive findings. One study found that handwriting changes can be observed at any level of alcohol — but concluded that none of the alterations in handwriting can be attributed to the effects of alcohol intake alone.

A second study charted handwriting deterioration in 35 men and women who provided samples both before and after drinking. The researchers concluded that handwriting could not be used in any way to accurately measure a writer’s blood alcohol concentration. These findings make handwriting evidence particularly vulnerable to challenge in court.

Hand Pat Test

The hand pat test requires the subject to place one hand palm-up in front of them. The other hand is placed on top with the palm facing down. The top hand then pats the bottom hand once and is rotated 180 degrees to pat the bottom hand with the back of the hand. This continues with the subject increasing speed as directed by the officer.

Some experts characterize the hand pat as a failure-designed test: because the subject must continually increase speed, most people will eventually double-pat or roll their hand rather than patting cleanly on each rotation as required. The test has not been scientifically validated as an accurate predictor of sobriety.

Picking Up Coins Test

Like the hand pat, the picking up coins test uses the hands rather than balance, which can be an advantage when a subject has reported a bad back, leg, or knee injury during pre-test questioning. The subject is asked to pick up several coins from a flat surface — such as the hood of a car — with one hand.

The test is rarely used. Like the hand pat, it has not been scientifically validated as an accurate predictor of sobriety or blood alcohol concentration.

The 5 cross-contamination attacks

1. The testing area is sloped.

Whether the particular test is the walk the line test, the Romberg test, or the one leg stand, it should be administered on a level surface. This is rarely the case because there is almost always a little gradient.

Sometimes the testing area actually slopes in two different directions.

Obviously, if the area was not level during the Romberg test, it did not suddenly become level during the one leg stand.

2. Lack of a baseline.

If the officer does not know how you would have performed on the field sobriety tests without the consumption of alcohol, a claim cannot validly then be made that poor performance was due to alcohol impairment.

Perhaps you are not particularly coordinated. You may have also been tired, or had some other reason (other than alcohol) for poor performance on a test.

3. The officer does not know the why of the test.

The prosecutor will tout the arresting officer’s knowledge, experience and training in administering and evaluating field sobriety tests because the state offers the police officer as an expert.

Your attorney may challenge this expertise by asking the officer why the test is administered in a certain manner. For example, few officers know the reasons why the head is tilted back and the eyes are closed in the Romberg test. For this reason the Romberg test is good place to use this cross-contamination dynamic.

4. Innocent reasons for poor performance.

Field sobriety tests are not easy for everyone. Fatigue, lack of coordination and stress are just of few of the many reasons to explain why someone did not perform well.

Your attorney may find that the horizontal gaze nystagmus test is a good time to introduce the notion that there are many reasons why you did not perform perfectly. The reason for this is that the horizontal gaze nystagmus test has a bevy of innocent reasons to explain a claim of failure on the test.

5. Complex instructions are given in a short period of time.

Most field sobriety tests have numerous requirements. Despite the complexity of many of the instructions, the tests are often explained and demonstrated only once, and in as little as ten to fifteen seconds. You are then expected to have an instant retention of the instructions. Rather than a test, this process takes on the onus of a “pop quiz.”

Your attorney might time how long the officer takes to give the instructions when the officer testifies about the instructions on direct examination. Then on cross-examination your attorney can ask the officer if the officer gave the instructions to you in the same manner as the officer just testified in court. The answer will probably be yes. Then your attorney might have the officer confirm that the instruction phase took all of fifteen seconds.

Then, in closing argument, your attorney might remind the jury how well you did on the field sobriety tests despite the brevity in which the complex instructions were given. Your attorney might ask the jurors if they themselves can recall the exact instructions of all the field sobriety tests. Furthermore, your attorney might remind the jurors that they have had the benefit of hours, not seconds, of time being spent in court discussing the field sobriety tests.

How the Prosecutor Will Respond to Attacks on Field Sobriety Testing

If the police officer claims that you failed one or more field sobriety tests, your attorney will attempt to raise reasonable doubt about the value of the test or the officer’s conclusions. The prosecutor is then likely to respond to these attacks in one or more of the following ways.

Promoting the National Highway Traffic Safety Administration

Assuming that the field sobriety tests were given pursuant to NHTSA protocols, the prosecutor is likely to emphasize the research that went into developing the standardized tests. The prosecutor will make the tests appear as scientific as possible in order to heighten their perceived accuracy and credibility with the jury. Understanding this tactic helps your attorney prepare to counter it — including by pointing out the significant limitations of even the NHTSA-validated tests when not administered under controlled conditions.

Promoting the Officer’s Training

The prosecutor will emphasize whatever specialized training the arresting officer received in field sobriety testing. This goes beyond basic police academy training — the prosecutor will make sure the jury knows the officer also received field training and may highlight the officer’s personal experience across hundreds or even thousands of DUI investigations. Your attorney’s role is to probe the depth of that training and expose gaps, particularly the officer’s inability to explain the scientific basis for the tests they administer.

Promoting the Officer’s Instructions

Assuming the officer gave the test instructions correctly, the prosecutor is likely to tell the jury that the instructions were explained carefully and accurately, and that the officer demonstrated the tests so you had ample opportunity to understand them. This is a direct counter to Attack #5 — the complexity of instructions given in a short time. Your attorney may use the timing strategy described above to challenge whether the instructions were truly adequate despite the prosecutor’s claims.

Correlating Tests to Alcohol Levels

The prosecutor may present an expert witness who has conducted correlation studies comparing field sobriety test performance with blood alcohol levels. If your performance on the tests is consistent with what would be expected at your tested BAC level, the prosecutor will have their expert emphasize this consistency to the jury. Your attorney can counter by challenging the validity of those correlation studies and by pointing out individual variables — physical condition, fatigue, anxiety, uneven surfaces — that the studies do not account for.

Discrediting Lay Witnesses

If you or any of your friends testify about how you performed on the field sobriety tests, the prosecutor will ask whether you or your witnesses have any specialized training in administering or evaluating field sobriety tests. The answer will almost always be no. The prosecutor will then argue that the jury should believe a trained officer over someone with no formal FST training. Your attorney can respond by noting that the officer’s “training” often amounts to learning to administer tests that the NHTSA itself has found to have significant reliability limitations.

Additional Defense Strategies Beyond Challenging the Tests

While attacking the validity of field sobriety tests and chemical test results are powerful defense strategies, a complete DUI defense often involves additional legal challenges unrelated to the tests themselves.

Challenging the Legality of the Traffic Stop

The Fourth Amendment protects drivers from unreasonable searches and seizures, including traffic stops. Law enforcement must have a reasonable suspicion of criminal activity — such as an observed traffic violation or visible signs of impairment — to lawfully justify stopping your vehicle. If your attorney can demonstrate that the officer lacked reasonable suspicion or probable cause, the evidence collected after that stop — including all field sobriety test results and chemical test results — may be suppressed as inadmissible in court.

Rights Violations During the Arrest or Testing Process

If your constitutional rights were violated at any point during the traffic stop, arrest, or subsequent testing — including failure to properly advise you of your rights or coercion in obtaining test consent — those violations can form the basis of a defense. Any evidence obtained through rights violations may be subject to suppression, potentially weakening or eliminating the prosecution’s case.

Legal Consequences of DUI Test Results in California

Failing a DUI test in California can lead to serious legal consequences. For a first-time DUI offense, penalties can include:

• Up to six months in county jail
• Fines of up to $1,000 (plus substantial penalty assessments that significantly increase this amount)
• A six-month driver’s license suspension
• Mandatory DUI school
• Probation, community service, and traffic school requirements even if jail time is avoided

Penalties increase significantly with subsequent offenses. Aggravating factors — such as causing injury or death, having a passenger under 14, or a very high BAC — can elevate charges to a felony. The severity of consequences depends on the specific circumstances, which is why challenging the test evidence that forms the basis of the prosecution’s case is so important.

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