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DUI Defense and SFST

SFST and Expert Testimony in DUI Defense

By: Lain A. Lawrence - DUI Defense Attorney Feb. 26, 2024

In 2019, the Colorado Supreme Court issued an order in Campbell v. Colorado. The ruling stated that a police officer must be an expert witness.

Prosecutors do this to permit discussion of horizontal gaze nystagmus (HGN). Officers observe HGN in one of the standard field sobriety tests during a DUI investigation. The opinion resulted in a change in the way DUI cases are litigated.

Law enforcement officers must now obtain certification as expert witnesses to provide opinions on HGN. Prosecutors seek to certify police officers as experts in HGN and standard field sobriety tests (“SFST”) in general.

The result is a Colorado DUI defense lawyer must understand the procedures of a DUI investigation. They need to be prepared to meet the officer as an expert and question them as such. This article will address some of the concerns seen from an expert witness on SFST.

How is an Expert Witness qualified under Colorado law?

The Colorado Rules of Evidence outline the method for certifying a witness as an expert. The rule provides:

“If scientific, technical, or other specialized knowledge will assist the trier of fact to understand the evidence or to determine a fact in issue, a witness qualified as an expert by knowledge, skill, experience, training, or education, may testify thereto in the form of an opinion or otherwise.”

C.R.E. 702.

The rules do not require an advanced degree or years of experience. Instead, the threshold for certifying an expert is relatively low. Law enforcement officers will typically undergo a 24 – hour class during their time at the academy. Their ongoing education requires a recertification to occur once every few years.

During litigation, prosecutors must endorse witnesses as experts. This requires them to disclose certain things to a DUI lawyer. The primary disclosures include curriculum vitals and a written statement expressing the opinion to be given.

What are SFSTs in a Colorado DUI?

Law enforcement perform SFSTs in many DUI cases.  These tests were established by the National Highway Safety Traffic Administration. They were created in the late 1970’s to assist police in DUI deduction and prosecution.

The tests are referred to as split attention tests. This means the tests are focused on a person ability to pay attention and physically do the tests. The idea is that driving requires a person to use split attention as well.

There are three tests that are generally used by the police. The first is the horizontal gaze test.

These tests require a defendant to focus on a stimulus. The stimulus is typically a pen. The officer will move the pen from the left of a defendant’s face to the right.

During the tests, an officer is looking for nystagmus. Nystagmus is the involuntary jerking of the eye as it moves. This is caused by alcohol’s effect on the nervous system.

The test is boiled down to 6 clues. A person will be considered impaired if they exhibit 2 of the 6 clues.

Police will then conduct the walk and turn test. This test requires a defendant to stand heel to toe during the instruction phase. A defendant will then take 9 steps forwards turn and take 9 steps back.

The investigator is looking for clues during the entire test. These clues include:

1.    Losing balance during instruction phase

2.    Taking to many/few steps

3.    Improper turn

4.    Starting too soon

5.    Missing heel to toe

6.    Stepping off the line

7.    Stopping while walking

8.    Raising arms during the walking portion.

The NHSTA has found that 2 of these 8 clues is sufficient to find a defendant did not complete the tests as a sober person would.

The final test used by the police is the one-legged stand test. This test requires a defendant to raise one leg six inches off the ground and count to thirty. Police are looking for the defendant swaying, using arms to balance, putting the foot down, or hopping. A person is considered to not perform the test as a sober person would if they exhibited 2 clues.

While these are the three core tests employed by police, the NHSTA permits other tests. 

Which tests determine impairment by drugs?

Colorado law defines a DUI as the operation of a motor vehicle while under the influence. Under the influence means intoxication caused by alcohol or drugs. Police use the three SFSTs discussed above during a driving under the influence of drugs investigation.

This is why they phrase testimony about the testing as "not completed by a sober person". The sober person includes not under the influence of alcohol and drugs.

This creates issues because a person impaired by marijuana or cocaine should perform differently than a drunk individual. Marijuana does not affect the nervous system like alcohol does and does not cause nystagmus.

In drug related investigations, the testing officer will employ additional tests. Juries commonly hear about the Modified Rhomberg Test.

The Modified Rhomberg Test requires a suspect to told to stand straight with feet together and arms down to their side. The person is told to tilt their head back and close their eyes while counting to 30. A suspect is instructed to stop the test once they have counted to 30 seconds.

Police look for three clues during the test. The officer will first look for swaying. A person may sway if they move more than 1 inch to one side or the other.

The second clue is tremors in the eyes or muscles. Tremors are attributed to substance use. Body tremors are attributed to stimulants and cannabis. Muscle tremors can be caused by stimulants, and eye tremors can be caused by cannabis.

The final clue is time. People consider time normal if it falls within five seconds of the target 30 seconds. A count of less than 25 seconds is indicative of a substance that accelerates the internal clock. Conversely, a count of over 35 seconds is indicative of a substance slowing down an internal clock.

The key flaw with the Modified Rhomberg Test is balance. Balance is impacted by three major factors, vision, feeling in the feet, and the vestibular system.

The vestibular system is the semicircular system in the inner ear. This system is why an ear infection cause a person to lose balance. Tilting your head back disengages this system. Closing your eyes results in 2 of the three factors impacting balance to be removed.

In essence, a defendant is placed in a position to have bad balance from the start of the test. This would be a problem for sober people. The other SFSTs have problems as well.

What are common problems of SFST?

A main concern with SFST is that they are not designed in a truly scientific fashion. Most DUI offenses involve an investigator contacting a defendant for the first time. The officer does not have a base level of how a defendant would perform if they were sober or not. 

Conducting these tests requires under a minute for each. The one-legged stand test for example takes 30 seconds to complete. The HGN test requires an officer to move the stimulus from side to side a few times, but each swipe must take approximately 4 seconds to move from one side to the center. 

Grading is also problematic. The walk and turn test is judged on 8 clues.

4 of the clues can be seen during the walking portion. A person can miss one heel to toe out of 16 steps and exhibit the clue. If a person misses heel to toe on all 16 steps it is still considered one clue.

In the simplest of mathematical terms, a person can exhibit one of the 4 walking clues 72 times during the 16 steps. Adding the other 4 clues gets 76 points at which time a clue can be seen.

If a person answers 2 questions incorrectly on a test, they might not be considered sober, even if they score 97%. This is because making mistakes on the test could indicate impairment. It is important to be fully alert and focused when taking a test to ensure accurate results.

Are SFST Valid Tests?

The NHSFST STA has conducted validation studies concerning SFSTs. Officers certified as experts testify concerning these studies. The general testimony is that they are found to be 91% reliable.

The studies have problems from a scientific approach. A Colorado validation study was conducted several years ago.

In that study, researchers followed police officers. They would observe police officers conduct DUI investigations and administer SFST. After arresting a suspect, the research would look at the individual’s blood alcohol concentration (“BAC”) to determine if the officer was correct in arresting the person or not. The researchers look at the blood alcohol content of breath tests and blood tests.

 This methodology causes problems in the validation process. First, a DUI investigation starts from the moment an officer observes bad driving until arrest. Officers will look for indicia of alcohol consumption, ask about alcohol consumption, and make several observations of suspected drunk drivers prior to the tests ever being requested. 

Law enforcement believes or knows a person is under the influence before requesting a test. A common tactic used during a DUI trial is having officers testify concerning their experience with using the tests and accuracy. However, the officers and test are not performed on suspects that are believed to be sober.

Understanding these issues in the validation study help to reveal flaws in any claims concerning the reliability of SFST.

Speak with a DUI Defense Attorney if You are facing an alcohol related offense in Colorado.

Understanding SFSTs is crucial for a criminal defense attorney. Knowing how to question an officer is extremely important during a trial. Each case and each defendant require a DUI lawyer to tailor a defense to their case and goals.

The criminal defense attorneys at our law office routinely handle DUI cases. We are knowledgeable with every aspect of DUI law. We provide representation for any type of case, and we handle DMV hearings to get restricted licenses.

Get a consultation today if you are charged with a DUI or DWAI in Aurora or Denver. We are open during normal hours and can stay late or be available on weekends if needed.

Schedule a free consultation with a Denver DUI Defense Attorney from the Lawrence Law Firm. We are ready, willing, and able to represent you. Our firm charges flat fees, but we also provide flexible payments plans. Your financial situation should not compromise your legal defenses.