What Do Cops Look For in a Field Sobriety Test?
When they administer the DUI eye test and other field sobriety tests, police officers look for clues that indicate intoxication. Usually, these clues are related to test performance or the ability to follow directions. Alcohol affects physical and mental abilities. Intoxicated persons cannot act or think straight.
Although the science behind FST clues, and the FSTs themselves, is shaky, most jurors readily accept these results. Many jurors don’t understand the difference between reliability and accuracy. If a Virginia DUI defense attorney explains the difference, without mansplaining it, jurors usually question FST results. If this questioning gives even one juror a reasonable doubt as to the evidence, the defendant is not guilty as a matter of law.
DUI Eye Test
Most officers start the three-test battery with the horizontal gaze nystagmus (HGN) test. This test has the highest compliance rate. In fact, many suspects don’t realize the HGN test is a DUI field test.
During the HGN test, officers look for involuntary pupil movements at certain viewing angles. About 80 percent of people who exhibit these involuntary movements have nystagmus.
The problem is that alcohol intoxication is not the primary cause, or even sole cause, of nystagmus. Usually, a childhood brain injury causes nystagmus. So, these individuals cannot pass the DUI eye test whether they’re drunk, sober, or somewhere in between.
Because of this weakness, many Loudoun County judges only allow prosecutors to use HGN results for limited purposes.
Walk-and-Turn
The WAT, or the walking-a-straight-line test, might be the signature DUI field sobriety test. The WAT has so many “clues” that it’s almost impossible to pass this test, at least in the officer’s opinion. These clues include:
- Starting the test before the officer says “start,”
- Beginning with the wrong foot,
- Swaying,
- Stumbling,
- Extending arms to maintain balance,
- Taking the wrong number of steps,
- A sloppy turn-around, and
- Ending the test before the officer says “stop.”
Footwear affects this test. It’s almost impossible to walk heel to toe in cowboy boots, dress shoes, flip-flops, or pretty much anything else except athletic shoes.
Environmental conditions, like flashing squad car lights, also affect this test. These flashing lights create a disorienting effect known as flicker vertigo. This effect also affects the HGN test, which was discussed above.
One-Leg Stand
Like the WAT, the OLS is a divided attention test. Scientifically, intoxicated people cannot follow directions and execute those directions. Alcohol impairs brain functions too badly.
Also like the WAT, the OLS has so many clues that most people cannot possibly pass this test, at least as far as the administration officer is concerned. These clues include:
- Starting the test before the officer says “start,”
- Elevating the wrong leg,
- Holding the elevate leg at the wrong angle,
- Failing to hold the leg steady,
- Extending arms for balance,
- Swaying, and
- Ending the test before the officer says “stop.”
Mental and physical fatigue affect this test, or whichever test officers administer last, especially if officers administer unapproved tests, like the reciting the ABCs test, before they administer the three approved ones.
Sometimes, a Leesburg criminal defense lawyer excludes the results of unapproved tests. Sometimes, attorneys allow prosecutors to use them, giving jurors the impression that police officers crossed the line during their DUI investigation.
Reach Out to a Detail-Oriented Loudoun County Lawyer
There’s a big difference between an arrest and a conviction in criminal law. For a confidential consultation with an experienced criminal defense attorney in Leesburg, contact Simms Showers, LLP, Attorneys at Law. We routinely handle matters throughout Northern Virginia.
Source:
nhtsa.gov/sites/nhtsa.gov/files/documents/sfst_ig_refresher_manual.pdf
