Standardized Field Sobriety Tests (SFSTs)

These tests measure someone’s ability to complete the test “in a manner consistent with a sober person.” When a person does something inconsistent with how a sober person would perform on the test, the officer notes that inconsistency. These inconsistencies are known as “clues.” Each test has a different number of possible clues. Any number of clues may be indicative of impairment, but generally the more clues the more likely the person is impaired.

In police reports, you will often see a numeric summary of a defendant’s performance, such as: “OLS: 2/3, WAT 4/8, HGN 6/6.” In this hypothetical example, the defendant showed 2 of 3 possible clues on the One Leg Stand, 4 of 8 possible clues on the Walk and Turn, and 6 out of 6 possible clues on the Horizontal Gaze Nystagmus test. A sober person with no disabilities would not be expected to show clues on any of these tests.

For a detailed guide to SFSTs, check out CDAC’s SFST Primer.

One Leg Stand

The One Leg Stand (OLS) requires a person to stand on one leg while counting.

Video of NHTSA’s Demonstration of OLS

There are 4 possible clues on the one leg stand:

1. 1. Sways
  2. Uses arms for balance
  3. Hops
  4. Puts foot down

Walk and Turn

The Walk and Turn (WAT) requires a person to walk, one foot in front of the other, in a straight line and back.

Video of NHTSA’s Demonstration of WAT

There are 8 possible clues on the WAT:

1. 1. Unable to maintain balance while listening to instructions
  2. Starts walking too soon
  3. Stops walking
  4. Steps off the line
  5. Misses heel to toe
  6. Uses arms to balance
  7. Loses balance or turns incorrectly
  8. Takes the incorrect number of steps

Horizontal Gaze Nystagmus

The Horizontal Gaze Nystagmus (HGN) test is used to detect involuntary jerking in the eyes caused by impairment.

Video of NHTSA’s Demonstration of HGN

There are 6 possible clues for the HGN, 3 per eye:

1. 1. Lack of smooth pursuit
  2. Distinct and sustained nystagmus at maximum deviation
  3. Nystagmus prior to 45 degrees

During the HGN test, officers also test for vertical gaze nystagmus. To testify at trial about HGN, caselaw requires an officer be qualified as an expert in administering the HGN test. The officer need not be qualified as an expert in the science of HGN, only in the administration of the test.

Evaluation of SFSTs

The OLS, the WAT, and the HGN tests are the only field sobriety tests that have been field-validated as reliable indicators of impairment. This means these tests have proven to be accurate indicators of impairment in the field when used by actual law enforcement officers. The National Highway Traffic Safety Administration reports that three field-validation studies in Colorado, California, and Florida demonstrated that officers using these three tests alone were able to correctly identify a BAC of .05 or higher 86% of the time and a BAC of .08 or higher 91% to 95% of the time. In addition, in 2005, Jack Stuster, Ph.D., also published a paper concluding that SFSTs are accurate, reliable, and fully validated for field use.

Advanced Roadside Impaired Driving Enforcement (ARIDE)

The ARIDE training curriculum offers police officers advanced, expert-level training in field-sobriety testing. The goal is to prepare officers to “observe, identify, and articulate the signs of impairment related to drugs, alcohol, or a combination of both, in order to reduce the number of impaired driving incidents, serious injury, and fatal crashes.” ARIDE Training Manual. This training does not substitute for Drug Recognition Expert training. Rather, it fills the gap between the training all officers receive on SFSTs and the training DREs receive. ARIDE certified officers learn how to use the SFSTs, other field sobriety tests, observations, and interviews to better assess drivers and make better decisions about whether to arrest someone for impaired driving. See id.

In addition to the SFSTs, ARIDE certified officers may employ other field sobriety tests as part of an impaired driving investigation. These tests include:

1. 1. Modified Romberg Balance (MRB)

Video of MRB Test

1. 1. Finger-to-Nose (FTN) Test

Video of FTN Test

1. 1. Lack of Convergence (LOC) Test

Video of LOC Test

For detailed information about these tests, check out CDAC’s Field Sobriety Test Information Sheets.

Body-worn Camera Recordings of SFSTs

Now that all officers in Colorado are required to wear body-worn camera during encounters with suspects, your jury can see for themselves how a defendant performed on SFSTs. The good news is that juries who see defendant’s clearly swaying, losing balance, falling over, obvious jerking of the eyes, etc. are likely to be convinced the defendant was impaired. The bad news is that juries may disregard an officer’s testimony about a defendant’s performance on SFSTs if the defendant doesn’t “look drunk” on body cam, no matter how reliable SFSTs may be. This is why you should find time to watch the body-worn camera, especially in close cases.

SFSTs are Searches Under the Fourth Amendment

SFSTs are considered a “search” under the Fourth Amendment and require either voluntarily consent or the presence of probable cause. People v. Young, 546 P.3d 625, 629 (Colo. App. 2024); People v. Carlson, 677 P.2d 310, 318 (Colo. 1984).