SFST Clues Explained — What Police Officers Look for During a Roadside Sobriety Stop

If you’ve ever been pulled over on suspicion of impaired driving — or simply want to understand how law enforcement operates at a roadside stop — you may be surprised at just how structured the evaluation process really is. Officers don’t rely on gut feelings alone. They follow a precise, standardized protocol with defined scoring criteria for every observation they make. This article walks through the full picture: how each test works, what officers are watching for, and where the Drug Recognition Evaluation process fits into the larger framework. All the information presented here is drawn directly from official standardized field sobriety test instructions and DRE evaluation guidelines used by law enforcement.

What Is an SFST?

It stands for Standardized Field Sobriety Test — a battery of roadside evaluations that trained police officers use to assess whether a driver is impaired. The “standardized” part is essential: every officer is trained to deliver the same instructions, in the same order, and to apply the same scoring criteria when deciding whether a driver has demonstrated a sign of impairment.

The standard battery consists of three core tests:

Beyond these three, additional evaluations — such as the Romberg Balance test and the Finger-to-Nose test — may also be used depending on the circumstances of the stop.

How Officers Deliver Instructions — and Why It Matters

One of the most important and often overlooked aspects of this evaluation process is exactly how officers communicate each exercise. The clue instructions for every test are standardized, meaning any deviation from the established script can affect the validity of the evaluation. Here is what those instructions look like in practice for each of the three tests.

HGN Instructions

For the eye evaluation, the officer instructs the driver to remove their glasses, keep their head completely still, and follow a moving stimulus — typically a pen or finger — with their eyes only. The officer makes clear: “Do not move your head.” The driver must verbally confirm they understand before the test begins.

The Walk and Turn, Step by Step

The Walk and Turn instructions are considerably more involved than most drivers expect. The driver is asked to place their left foot on a line, put their right foot directly in front of it with the right heel touching the left toe, and keep both arms at their sides. They must wait for the command to start. When told to begin, they take nine heel-to-toe steps along the line, turn around by taking several small steps while keeping one foot on the line, and return nine heel-to-toe steps. Throughout, they must watch their feet at all times, keep their arms at their sides, and count each step out loud. The officer demonstrates the movements, and the driver confirms they understand the directions at two separate points — once after the initial walkthrough and again after the turn is demonstrated.

One-Leg Stand Instructions

For this test, the driver stands with heels together and arms at their sides. When instructed, they raise one leg — either leg — approximately six inches off the ground, foot pointed outward, keeping both legs straight while looking at the elevated foot. They count aloud: “one thousand and one, one thousand and two, one thousand and three,” continuing until told to stop.

The Eye Test: What Officers Are Really Watching

The Horizontal Gaze Nystagmus evaluation is based on the involuntary jerking of the eyes that becomes exaggerated when a person is impaired. There are six HGN clues in total — three scored for each eye. Officers watch for the following in each eye, separately:

  1. Lack of smooth pursuit — the eye does not track the moving stimulus smoothly and instead jerks as it follows
  2. Distinct and sustained nystagmus at maximum deviation — noticeable eye jerking when the eye is held at the outermost edge of its range
  3. Angle of onset prior to 45 degrees — eye jerking begins before the stimulus even reaches a 45-degree angle from center

It is worth noting that the standardized HGN protocol includes no specific scored clues for vertical nystagmus. That is addressed separately as part of the Drug Recognition Evaluation process described later in this article.

How Many Clues in Walk and Turn?

The Walk and Turn Test is the most frequently asked-about of the three standardized evaluations, and the most common question surrounding it is also the most practical: what is the official number of scored clues? The official answer is eight total — divided across two distinct phases of the test.

Some searches online turn up references to FST 7 legs, but the actual protocol is clear: there are 8 total Walk and Turn clues, with 2 scored during the instruction phase and 6 scored during the walking phase itself.

Here is the complete breakdown of clues for Walk and Turn Test scoring:

Phase Clue # What the Officer Is Watching For
Instruction Phase 1 Cannot keep balance while listening to instructions
Instruction Phase 2 Starts walking before being told to begin
Walking Phase 3 Stops while walking
Walking Phase 4 Misses heel to toe
Walking Phase 5 Steps off the line
Walking Phase 6 Uses arms to balance
Walking Phase 7 Improper turn
Walking Phase 8 Wrong number of steps

What makes the SFST Walk and Turn clues particularly revealing is how the instruction phase is designed. Being unable to hold the starting position while simply listening to directions — before a single step is taken — is itself an indicator of divided attention difficulty, a key marker of impairment.

When reviewing Walk and Turn Test clues from this perspective, the two instruction-phase observations are often underappreciated but carry real weight in the overall scoring picture.

One-Leg Stand: Four Observations That Count

Compared to the Walk and Turn, One Leg Stand clues are fewer but no less significant. The test requires the driver to hold one foot raised approximately six inches off the ground while counting aloud, continuing until told to stop. Officers score exactly four One Leg Stand Test clues:

  1. Swaying while balancing
  2. Using arms to balance
  3. Hopping to maintain balance
  4. Putting the raised foot down before being told to stop

Despite its apparent simplicity, the one-leg stand simultaneously tests balance, concentration, and the ability to follow multi-step instructions under the pressure of a traffic stop — all at once.

Other Field Sobriety Tests You May Encounter

Beyond the three standardized evaluations, officers may also administer two supplemental tests:

What Does DRE Mean in Police Work?

When a driver appears impaired but registers a low or zero breath alcohol reading, a specially trained officer may be called in. Understanding the DRE meaning police use clarifies this role: DRE stands for Drug Recognition Evaluator (also referred to as Drug Recognition Expert). These officers are trained to conduct a comprehensive 12-step evaluation protocol that extends far beyond the standard roadside FST battery.

Here is how the DRE process unfolds, step by step:

  1. Breath Alcohol Test — If the breath alcohol content (BrAC) is below the per se limit but impairment still appears to exist, the DRE evaluation continues.
  2. Interview of the Arresting Officer — Because the arresting officer may not have specialized DRE training, the DRE officer collects that officer’s field observations, statements, and any other relevant information about the stop.
  3. Preliminary Examination (1st Pulse) — The subject’s general behavior is observed, any medical conditions are noted, and the first of three pulse readings is taken.
  4. Eye Examination — This step covers horizontal gaze nystagmus, a VGN test (vertical gaze nystagmus), and a convergence evaluation. The Lack of Convergence Test assesses whether the eyes can properly converge — that is, cross toward each other — as a stimulus moves close to the face. A deficit here can be a relevant finding in the overall evaluation.
  5. Divided Attention Psychophysical Tests — Evaluations including the Romberg, walk-and-turn, one-leg-stand, and fingertip-to-nose tests are administered.
  6. Vital Signs (2nd Pulse) — Blood pressure, body temperature, and a second pulse reading are recorded.
  7. Dark Room Examination — Pupil size and light responses are measured under controlled lighting conditions, and the nose and mouth are examined for signs of drug use.
  8. Muscle Tone Check — The muscle tone of the subject’s arms — specifically the biceps and forearm — is assessed.
  9. Check for Injection Sites (3rd Pulse) — The subject’s arms, legs, and other body parts are examined for injection marks. The third and final pulse measurement is taken at this stage.
  10. Interrogation — The subject is given the opportunity to make statements or acknowledge drug use, and the DRE officer may present their observations at this point. For those who have encountered a Phase 10 instructions PDF or similar law enforcement reference document, this interrogation step is the formal component that notation corresponds to in the 12-step sequence.
  11. Opinion of the Evaluator — The DRE generates a professional opinion as to whether the subject is drug-impaired and, if so, which category or categories of drugs are involved.
  12. Toxicological Examination — A biological sample — blood, urine, or breath — is collected for forensic laboratory analysis to confirm or challenge the evaluator’s opinion.

Normal Ranges Used During the DRE Process

At multiple stages of the DRE evaluation, physiological measurements are compared against established normal baselines. These ranges help identify readings that fall outside what would be expected for an unimpaired individual.

Pupil size standards have been updated based on research published in Clinical Research (Volume 75, Number 3, March 2004). The earlier single-range standard of 3.0–6.5 mm is no longer in use. Instead, pupil size is now evaluated in the context of the current lighting conditions, which significantly affect normal pupil diameter. The updated criteria are as follows:

Lighting Condition Mean Pupil Size (mm) Median Pupil Size (mm) One Standard Deviation (mm)
Room Light 3.86 3.62 0.93
Near Total Darkness 6.41 6.45 1.55
Direct Light 3.35 3.40 0.72

This updated approach reflects how significantly ambient lighting affects normal pupil diameter — a nuance the earlier fixed range completely failed to capture.

Why Standardization Is the Whole Point

Standardized field sobriety tests and the Drug Recognition Evaluation process are built on layers of structure: precise instructions, defined scoring criteria, measured physiological baselines, and a multi-step confirmation protocol. From the six scored eye observations in the HGN evaluation to the eight-clue Walk and Turn battery to the four indicators in the one-leg stand — every element exists for a reason, and every officer is expected to apply it the same way.

Understanding that structure doesn’t just satisfy curiosity. It provides a clearer picture of how law enforcement makes consequential decisions during roadside stops, and why the consistency of these procedures matters so much to the integrity of the entire evaluation process.