Can I refuse field sobriety tests?

In most states including Virginia, [def:field sobriety tests] (walk-and-turn, one-leg stand, HGN) are voluntary — they are not covered by the [def:implied consent] statute [§ 18.2-268.2], which applies to chemical tests. However, refusal may affect the officer's decision to arrest and can be noted in the report.

Are breath tests accurate?

Breath testing devices estimate BAC from exhaled air. While generally accepted by courts, they can be challenged based on calibration records, operator error, mouth alcohol contamination, medical conditions, and the time between the stop and the test.

What if my BAC was below 0.08?

A BAC below the per se limit does not prevent prosecution [§ 18.2-266]. The state can still pursue a DUI/DWI charge based on impairment from alcohol, drugs, or a combination — the per se limit is just one way to prove the offense.

Can blood test results be challenged?

Yes. Blood tests can be challenged on grounds including improper collection procedures, chain of custody issues, contamination, fermentation of the sample, and the time elapsed between the stop and the blood draw.

Topic guideUpdated 2026-02-27

Virginia DUI Testing — Field Sobriety, Breath & Blood

What evidence may be involved.

Evidence in DUI/DWI cases in Virginia comes from three sources: officer observations, Field sobriety tests, and chemical tests (breath, blood, or urine) §18.2-266. Each type of evidence has specific legal requirements and potential weaknesses.

Officer observations

The officer's report documents: the reason for the stop, driving behavior (weaving, speed, failure to signal), physical observations (odor of alcohol, bloodshot eyes, slurred speech), and the driver's demeanor and statements. These observations form the basis for probable cause.

Standardized field sobriety tests (SFSTs)

Three standardized field sobriety tests have been validated for use in DUI enforcement §NHTSA SFST Manual:

Horizontal Gaze Nystagmus (HGN)

The officer observes the eyes as the driver follows a stimulus (pen or finger). Involuntary jerking of the eye at certain angles can indicate impairment. This is the most validated SFST, but it must be administered according to specific protocols.

Walk-and-Turn

The driver takes nine heel-to-toe steps along a line, turns, and takes nine steps back. The officer watches for specific "clues" of impairment: starting too soon, losing balance, stepping off the line, using arms for balance, incorrect number of steps, or improper turn.

One-Leg Stand

The driver stands on one foot with the other raised approximately six inches off the ground while counting for 30 seconds. Clues include swaying, using arms for balance, hopping, or putting the foot down.

💡Field sobriety tests are designed for controlled conditions. Uneven pavement, poor lighting, footwear, medical conditions, age, and weather can all affect performance. These factors can be challenged in court.

Chemical tests §18.2-268.2

Breath tests

Breath testing devices (such as the Intoxilyzer or DataMaster) estimate BAC by measuring alcohol in exhaled breath. These machines must be properly calibrated and maintained, and the operator must follow specific protocols. Common challenges include mouth alcohol contamination, improper observation periods, and machine malfunction.

Blood tests

Blood tests are considered the most accurate method of measuring BAC. However, they require proper collection, handling, and chain of custody. Challenges can include improper swab use (alcohol-based swabs), fermentation of the sample, and delays between the stop and the blood draw.

Urine tests

Urine testing is the least common and least reliable method for measuring BAC. It is sometimes used when breath and blood tests are unavailable, particularly in drug-impaired driving cases.

The per se limit and what it means

Virginia's per se BAC limit is 0.08 §18.2-266. "Per se" means that a BAC at or above this level is itself sufficient to establish the DUI/DWI offense — the state does not need to prove actual impairment separately. However, a BAC below the per se limit does not prevent prosecution if there is other evidence of impairment.

✓Every piece of evidence in a DUI/DWI case can be challenged. Machine calibration records, officer training certifications, video footage, and the specific conditions of the stop and testing are all potentially relevant to the defense.

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