In most cases when a motorist has been detained for a traffic violation and is suspected of drunk driving, the investigating officer will request the suspect to perform certain field sobriety tests (FSTs). These are tests of coordination and mental acuity designed to see if the suspect’s performance correlates with certain indicators or signs of impairment due to alcohol or to certain types of drugs.
In addition to testing your physical agility, they test your ability to follow instructions. They will give you a series of instructions and if you miss any of the steps in the process, you will be deemed to have “not performed as explained and demonstrated.”
The officer’s observations of your performance on the FSTs will be on any police report and testified to at trial if your case proceeds that far as constituting at least circumstantial evidence of your impairment1.
An officer’s suspicion of intoxicated or impaired driving is usually raised after having observed your car weaving, travelling erratically or for violating a traffic law, which gives the officer probable cause to stop you. Other indicia of impairment include the officer detecting an odor of alcohol or marijuana on the your breath or person when the officer has approached and evaluated you in your vehicle.
Additional indications of possible drinking include your slurred speech, red face, bloodshot eyes, inappropriate or incoherent responses to questions, or after having noticed a container of alcohol in the car.You may also have responded affirmatively to an officer’s inquiry as to whether you had been drinking.
Under these circumstances, an officer will generally ask you to perform certain tests at the scene.
Motorists suspected of DUI are not required to submit to any FST and your refusal to perform any of these tests will not result in any criminal or civil penalties, including losing your driver’s license since this is not a violation of the state’s implied consent law. There is an exception for drivers who are on probation for drunk driving or if you are under the age of 21. If on probation, a refusal can result in revocation of your probation and possible jail time. If you are under 21, your refusal can result in loss of your driver’s license. Otherwise, there is no reason for you to agree to perform any field sobriety test.
An officer’s determination that a suspect is under the influence of alcohol or drugs bases on FSTs, whether standardized or not, are largely subjective. One of the factors that largely affects a suspect’s performance on an FST is the conditions under which the test is administered.
Studies that indicate how reliable FSTs are in detecting impairment or a suspect’s BAC of at least 0.08% are conducted under laboratory settings. The “suspects” know that they are not subject to arrest, imprisonment, or loss of driving privileges. A true suspect who agrees to perform any of these tests is understandably anxious and under extreme pressure. Most people under such conditions will be sweating profusely, have a racing heartbeat, and be worrying about the consequences of not adequately performing on these tests. Under these conditions, most individuals would have trouble concentrating on the numerous instructions being given to them and then following them correctly, whether they have alcohol to drink or not. Real-life conditions are difficult to duplicate in any laboratory setting and can have a profound effect on how a person performs.
Also, these studies are not conducted under real-life conditions on the open roadway. Weather and other conditions at the site of the traffic stop that can impact performance and lead an investigating officer to conclude that certain signs or clues of impairment are being exhibited include:
- Performing FSTs on uneven surfaces
- Windy conditions or possible precipitation
- Rush of traffic with bright lights, horns, and other traffic sounds
- Shoes that may not be conducive to walking in a straight line or standing straight
Standardized tests have the backing and support of the scientific community as to its reliability, at least to some extent. It also means that the officers who administer these tests must do so according to a published or established protocol or their validity will be attacked. California courts allow an officer to testify that a defendant’s poor performance on a standardized FST indicates a blood alcohol concentration (BAC) level of at least 0.08% or higher, though this is not a mandatory presumption2.
There are 3 standardized field sobriety tests that are accepted as reliable indicators of impairment:
- Horizontal gaze nystagmus
- One-leg stand
One standard test and commonly used FST used by many officers is the HGN or horizontal gaze nystagmus test, which does not require the suspect to perform any coordination or balance tests. It is considered one of the more reliable indicators of intoxication and an officer may testify as to his or her observations as indicating that the suspect was under the influence so long as a proper foundation is established by the prosecution3.
The test generally consists of the officer holding a pencil, penlight or other object known as a stimulus in front of your eyes and asking you to track it as he or she moves it from side to side. The officer is looking for the angle at which your pupil starts jerking involuntarily (nystagmus). If the jerking occurs at or before a 45 degree angle, it is supposed to be an indication of a BAC of at least 0.10%. The officer who administered the test and observed this phenomenon may testify that this is evidence the suspect’s BAC is at least 0.10%, though he or she may not give a quantitative number4. According to this test, the more intoxicated you are, the sooner your eyes will begin to jerk as your pupils move from side to side.
This particular test requires you to take 9 steps while walking heel-to-toe in a straight line. After the ninth step, you are instructed to pivot on one foot and return in the same manner to your starting position. The officer administering the test is first supposed to demonstrate the test.
The test has 8 indicators of possible impairment that an officer is to be observing:
- Did you maintain your balance while listening to the officer’s instructions
- You began walking before the officer has finished giving you the instructions
- Whether you stopped at any time to regain your balance
- You failed to touch your heels while walking
- You stepped off the line
- You used your arms to maintain balance
- You lost your balance while turning
- You took more or less than 9 steps
Should you exhibit at least 2 of these indicators, the officer will conclude that you are impaired.
The Walk-and-Turn test is a test of divided attention, designed to see if you can simultaneously listen to and follow the instructions given. This tests both your mental and physical capabilities.
In this FST, an officer will instruct you to stand with one foot about 6 inches off the ground and to count in thousands–one thousand one, one thousand two and so forth until your reach 30 or the officer advises you to stop. While standing, you are supposed to focus on your raised foot and to keep you arms and hands by your sides. The officer is to personally demonstrate how the test is performed.
This is another divided attention test where an officer observes your ability to follow the instructions given and to perform them without losing your balance or performing some other movement that was not part of the officer’s instructions.
Similar to the HGN test, the officer is required to look for 4 possible clues of impairment:
- You swayed side to side or back and forth while on one foot
- You used your arms for balance
- You hopped
- You were unable to keep your foot up–if at least 3 times, then this is a failure
Field sobriety tests are used to determine impairment based on alcohol consumption and not necessarily on the ingestion or administration of controlled substances or prescription medication that can lead to impairment. A 2013 study by the Canadian Centre on Substance Abuse of the 3 standardized field sobriety tests revealed that they do have validity when officers administering the tests suspect that a motorist is under the influence of a drug. However, these tests are not so reliable when it comes to classifying the suspected drug.
Regarding the HGN (gaze nystagmus), users of CNS depressants (sleeping pills, tranquilizers, barbiturates, quaaludes) were found to more likely exhibit distinct nystagmus at maximum deviation than non-drug users. Researchers found that 88% of of persons who exhibited 4 or more clues had a BAC of at least 0.08%. The breakdown for correctly classifying a drug was 94.6% for CNS stimulants (methamphetamines, cocaine, Ecstasy), 70.1% for CNS depressants, 0% for narcotic analgesics, and 1% for cannabis.
On the OLS, or one-leg stand test, about 83% of those who exhibited at least 2 of the 4 clues of intoxication were tested at 0.08% or higher. If based on the 4 clues, only 43.6% of cases correctly classified drugs with CNS stimulants at 59.9%, cannabis at 55.4% , and narcotic analgesics at 10.6%. No CNS depressants were correctly classified.
For the WAT test, or walk and turn test, there were 8 signs of impairment. Researchers concluded that 79% of those who exhibited at least 2 signs of impairment had a BAC of at least 0.08%. However, the classification for CNS stimulants was correctly estimated at 72.2%, cannabis at 39.7%, CNS depressants at 9% and narcotic analgesics at 3.5%.
Researchers on the Canadian study still felt that the results showed that CNS stimulants and depressants, narcotic analgesics, and cannabis were associated with impairment on the 3 standardized FSTs. Cannabis affected performance on only the OLS test and not on the HGN and WAT.
Additional Field Sobriety Testing Information
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