Field sobriety tests are often presented as objective measures of impairment, but they are performed on the side of the road by a person who has just been stopped, often at night, under flashing lights, with traffic nearby. Balance, coordination, and divided attention can be affected by anxiety, fatigue, injuries, footwear, age, medical conditions, uneven pavement, weather, or difficulty understanding the officer’s instructions.
The most important evidence is frequently the video. A police report may reduce a several-minute encounter to a list of “clues,” while body-worn or dash-camera footage shows how the driver actually walked, spoke, followed instructions, and interacted with the officer. Kevin Kennedy uses that objective record to test whether the field sobriety conclusions are justified.
Field Sobriety Tests Are Evidence, Not a DUI Element
Tennessee’s DUI statute, § 55-10-401, does not require the State to prove that a driver failed field sobriety tests. The tests are investigative tools officers may use when deciding whether there is probable cause and prosecutors may later use as circumstantial evidence of impairment.
A person can be arrested without performing the tests, and a poor performance does not automatically establish guilt. The ultimate question remains whether the State can prove DUI beyond a reasonable doubt.
The Three Common Standardized Tests
Officers frequently use the horizontal gaze nystagmus test, the walk-and-turn test, and the one-leg-stand test. The latter two require a person to listen to instructions, remember multiple tasks, maintain balance, and perform specific physical movements while being observed.
How the test is explained and demonstrated matters. A driver should not be judged for failing an instruction the officer did not clearly give.
Walk-and-Turn Conditions Can Affect Performance
The walk-and-turn test assumes a reasonably suitable surface and sufficient room. Sloped shoulders, gravel, wet pavement, darkness, traffic, debris, or an indistinct line can make the test harder even for a sober person.
Footwear, knee or back problems, age, weight, and recent injury may also affect balance. Video can reveal whether the testing location was appropriate.
The One-Leg Stand Is Physically Demanding
Standing on one leg while counting and keeping the arms down requires balance and concentration. A person with ankle, hip, back, neurological, or vestibular problems may struggle regardless of alcohol or drug use.
The defense should review whether the officer asked about medical limitations, whether the driver disclosed any, and whether the test was continued despite an obvious physical problem.
Horizontal Gaze Nystagmus Has Its Own Limits
Horizontal gaze nystagmus involves observation of eye movement while the subject follows a stimulus. The reliability of the officer’s conclusion depends on proper administration and on distinguishing alcohol-related nystagmus from other possible causes.
Because a camera often cannot capture the subtle eye movement itself, the jury may be asked to rely heavily on the officer’s testimony about what was seen. Training, procedure, positioning, timing, and alternative causes can therefore matter.
Instructions and Demonstration Should Match Training
Field sobriety tests are most useful when administered in a standardized way. Rushed instructions, interruptions, incorrect demonstrations, inconsistent counting directions, or failure to provide a proper starting position can affect performance.
The defense should compare the officer’s administration with the procedures the officer was trained to use and with what the report claims happened.
Nervousness Can Look Like Impairment
A traffic stop can make a sober person visibly anxious. Trembling, talking quickly, asking repeated questions, or forgetting an instruction can reflect stress rather than intoxication.
The full interaction matters. A driver who produces documents, answers questions appropriately, uses a phone normally, walks without difficulty, and communicates clearly may present evidence inconsistent with the officer’s impairment conclusion.
Drug DUI Can Complicate Field Testing
Field sobriety tests were developed primarily in the context of alcohol impairment. In drug cases, officers may use the same tests along with additional observations or a drug-recognition evaluation.
A particular drug may affect behavior differently from alcohol. The defense should avoid allowing a generic claim of “failed sobriety tests” to replace analysis of what substance was allegedly involved and whether the observed signs are scientifically consistent with impairment.
Refusing Field Sobriety Tests Is Different From Implied Consent
Roadside field sobriety exercises are different from the statutory rules governing breath and blood testing. Declining field sobriety exercises does not itself create the implied consent license revocation imposed for refusing a properly requested chemical test.
The officer may still consider the totality of circumstances in deciding whether to arrest, and the State may still prosecute DUI based on other evidence.
How Kevin Kennedy Defends Field-Sobriety DUI Cases
Kevin reviews the video frame by frame, paying attention to the testing surface, lighting, traffic, instructions, demonstrations, medical issues, footwear, interruptions, and whether the driver’s actual movements match the officer’s written description.
He then places the field testing beside the rest of the evidence rather than allowing it to dominate the case. If you are charged with DUI involving field sobriety testing in Nashville or Middle Tennessee, contact Kevin Kennedy Law Firm for a free, confidential consultation.
Legal references: Tenn. Code Ann. §§ 55-10-401, 55-10-406, and 55-10-407. This page is general information, not legal advice.