Field Sobriety Tests in Massachusetts

What Are Field Sobriety Tests?

Field sobriety tests are physical and cognitive tasks that a police officer asks a driver to perform during a traffic stop. Officers use the results to help them decide whether there is probable cause to arrest someone for operating under the influence.

In Massachusetts, police typically use five main tests to evaluate impairment:

These tests are designed to detect physical or mental signs of impairment. They are not meant to confuse or trick a person—but factors like nerves, medical conditions, uneven pavement, and poor weather can all affect performance.

NHTSA-Approved vs. Non-Approved Tests

The National Highway Traffic Safety Administration (NHTSA) has established scientific standards for field sobriety testing. However, only three of the five common tests have been validated by the NHTSA:

The alphabet test and finger-to-nose test do not meet NHTSA standards. A skilled defense attorney can argue that results from non-validated tests should carry little or no weight as evidence, since they haven’t been scientifically proven to accurately indicate impairment.

Even the NHTSA-approved tests must be administered exactly according to protocol. Deviations in instructions, demonstration, scoring, or environmental conditions can render results unreliable.

Landmark Massachusetts Case Law

Massachusetts has unique case law that significantly impacts how field sobriety test evidence can be used in court. Two landmark decisions provide critical protections for defendants:

Commonwealth v. Sands (1997)

The Massachusetts Supreme Judicial Court ruled that the Horizontal Gaze Nystagmus (HGN) test cannot be admitted as evidence unless its reliability is thoroughly established and the officer administering it is duly qualified. This creates a high evidentiary bar—prosecutors must prove the test was properly administered by a trained officer before results can be considered.

Together, these cases mean that police must meticulously follow established guidelines for FSTs to qualify as reliable evidence, and your refusal to participate cannot be held against you.

The Horizontal Gaze Nystagmus (HGN) Test — What the Officer Is Actually Looking For

The HGN test asks the officer to move a stimulus (a pen or fingertip) slowly across the driver’s field of vision while watching for involuntary jerking of the eyes. The NHTSA manual identifies six clues — three per eye — and an officer who counts four or more clues is trained to score the test as “impairment indicated.” The six clues are:

• Lack of smooth pursuit in each eye as it follows the stimulus
• Distinct and sustained nystagmus at maximum deviation (eye held at the far edge of vision for at least four seconds)
• Onset of nystagmus prior to 45 degrees from the center

The problem: nystagmus is caused by far more than alcohol. Vestibular disorders, head trauma, prescription medications (anti-seizure, anti-anxiety, antihistamines), eye conditions, fatigue, flashing emergency lights, and even pre-existing physiological nystagmus all produce clues that look identical to alcohol-induced nystagmus to an officer with only basic training. In Massachusetts, under Commonwealth v. Sands, the HGN is not admissible at trial unless the Commonwealth lays a foundation that the test was administered by a properly trained officer and that the underlying science is reliable in this case — a foundation prosecutors frequently cannot establish without calling an expert witness.

The Walk-and-Turn Test — Eight Clues, Two Phases

The Walk-and-Turn (WAT) is a divided-attention test in two parts: an instruction phase (standing with one foot in front of the other, heel-to-toe, while listening to instructions) and a walking phase (nine heel-to-toe steps on a line, a specified turn, and nine steps back). NHTSA recognizes eight clues, and two clues are enough for the officer to mark the test as “impairment indicated.” The eight clues are:

• Cannot keep balance during instructions
• Starts too soon before instructions are completed
• Stops while walking to steady themselves
• Does not touch heel-to-toe (gap of more than half an inch)
• Steps off the line
• Uses arms to balance (raised more than six inches)
• Improper turn (wrong number of small steps, turns the wrong way, or pivots)
• Incorrect number of steps

The NHTSA validation studies expressly limit the WAT to subjects under 65, weighing less than 50 pounds overweight, and not wearing heels over two inches. The test is not validated for people with leg, back, or middle-ear injuries. Officer testimony that “the driver missed heel-to-toe twice” is meaningless if the test was given on a sloped shoulder, in the rain, in dress shoes, after a back injury, or after midnight when the driver is exhausted. Every one of these is grounds to cross-examine the officer and ask the jury to disregard the test.

The One-Leg Stand — A 30-Second Test With Four Clues

The One-Leg Stand (OLS) requires the driver to stand on one leg with the other foot raised six inches off the ground, count out loud (“one thousand one, one thousand two,” etc.) for 30 seconds, and keep arms at the sides. NHTSA recognizes four clues, and two clues constitute “impairment indicated.” The four clues are:

• Sways while balancing (side-to-side or front-to-back)
• Uses arms to balance (raised more than six inches)
• Hops to maintain balance
• Puts foot down before 30 seconds are up

The OLS is the most physically demanding standardized test and has the highest false-positive rate. Like the WAT, the NHTSA validation studies excluded subjects who were over 65, 50+ pounds overweight, or wearing heels. Anyone with knee, hip, back, or balance issues will produce the same clues whether sober or impaired. Inner-ear conditions (BPPV, Ménière’s) and even a sustained stretch of recent inactivity produce false positives at the side of the road.

Practical reality: the average person, sober, in a controlled environment, fails one or more clues on the OLS roughly one-third of the time. Doing it at midnight on the shoulder of a state highway, in front of a uniformed officer with flashing lights behind you, makes the test even less reliable.

Medical, Environmental, and Procedural Factors That Affect FST Performance

The NHTSA manual itself warns that field sobriety tests are not infallible. The following non-alcohol factors commonly produce clues that look identical to impairment:

Medical Conditions

• Inner-ear disorders — BPPV, Ménière’s, vestibular migraine all cause balance failure that looks like alcohol
• Neurological conditions — multiple sclerosis, prior stroke, concussion history, Parkinson’s
• Musculoskeletal — knee replacement, hip injury, lower-back pain, plantar fasciitis
• Eye conditions — lazy eye, strabismus, contact lenses, glaucoma, recent LASIK surgery
• Diabetes / hypoglycemia — low blood sugar produces symptoms (confusion, slurred speech, poor coordination) virtually indistinguishable from intoxication
• Medications — anti-anxiety, anti-seizure, sleep aids, blood-pressure medications, and many over-the-counter products affect nystagmus and coordination

Environmental and Procedural Factors

• Surface — slope, gravel, broken pavement, wet leaves, or ice make heel-to-toe steps and one-leg balance nearly impossible
• Footwear — heels, boots, flip-flops, dress shoes
• Lighting — police cruiser flashing lights, headlights pointed at the driver, the angle of the moon, and rain on the windshield all interfere with nystagmus observation
• Weather — rain, snow, high wind, cold
• Time of day — fatigue and circadian rhythm impairment late at night
• Improper instruction — officers routinely deviate from the NHTSA-required script, demonstrate the test incorrectly, or fail to ask whether the driver has any medical conditions before administering it

How an Attorney Can Challenge FST Evidence

An experienced OUI defense attorney will scrutinize every aspect of how field sobriety tests were conducted. Common challenges include:

• Improper administration — Officer failed to follow NHTSA standardized procedures
• Environmental factors — Uneven pavement, poor lighting, inclement weather, or heavy traffic conditions
• Medical conditions — Inner ear disorders, leg injuries, neurological conditions, or medications can mimic impairment
• Non-validated tests — Alphabet and finger-to-nose tests lack scientific backing
• Officer qualifications — Insufficient training in NHTSA-standardized testing methods
• Age, weight, or physical limitations — These factors can significantly affect test performance without any impairment

If an officer testifies about a non-approved test, a knowledgeable attorney can object and seek to have that evidence excluded. Where officers deviated from NHTSA protocols, the attorney can argue the results are invalid.