A drink-driving prosecution is not one allegation but a chain of them, and every link has technical requirements. The stop must be lawful. The investigation must follow protocol. The sample must be collected and analysed correctly. And in some states — South Carolina notably among them — the whole encounter must be recorded on video, with the recording produced.
This guide breaks the offence into its elements and explains what has to be established for each.
Key Takeaways
- Many states separate two offences: driving while impaired, and driving with a prohibited alcohol concentration. They are proved differently.
- South Carolina imposes a statutory video recording requirement covering both the roadside encounter and the breath testing room.
- Field sobriety tests are standardised procedures with defined administration rules and known limitations.
- Breath testing depends on instrument certification, operator qualification and a pre-test observation period.
- Penalties in several states escalate by alcohol concentration tier, not merely by whether the limit was exceeded.
The Legal Definition
The core offence generally requires proof that the defendant drove or operated a vehicle while their faculties were materially and appreciably impaired by alcohol, drugs, or a combination.
Two elements deserve attention. Operation can extend beyond driving on a road — being in physical control of a vehicle, in some circumstances while stationary, may suffice depending on the jurisdiction. Impairment is a question of faculties, which is why a prosecution can proceed even where no alcohol reading is available at all, resting instead on driving behaviour, observations and performance on testing.
South Carolina illustrates a structure used in various forms elsewhere: alongside the impairment offence sits a separate offence of driving with an unlawful alcohol concentration. The second does not require proof of impaired faculties — the reading itself is the offence. A defendant may face both, and they succeed or fail on different evidence.
Alcohol Concentration and What It Proves
Blood alcohol concentration is the familiar measure, with 0.08 the general threshold for adult drivers, 0.04 for commercial licence holders, and near-zero thresholds for drivers under 21 in most states.
South Carolina’s treatment of the reading in the impairment offence is worth understanding, because it is not a simple per se rule. The statute sets out inferences: a low reading supports an inference that the driver was not under the influence, an intermediate range creates no inference either way, and a reading at or above the threshold supports an inference that they were. Inferences are rebuttable, which leaves room for argument that a per se framework would not.
Penalties then escalate by tier. Rather than a single penalty for exceeding the limit, fines and custodial exposure step up across concentration bands, so the difference between a reading just over the threshold and one substantially above it is significant.
Field Sobriety Testing
Three standardised tests are used: horizontal gaze nystagmus, the walk-and-turn, and the one-leg stand. Each has a defined administration protocol and a defined set of scored indicators.
They are also more contestable than most people assume. Performance is affected by footwear, road camber and surface, weather, lighting, passing traffic, age, weight, fatigue, injury and a range of medical conditions including inner ear disorders and neurological problems. Nystagmus in particular can have causes unrelated to alcohol.
Because these are scored procedures rather than impressions, departures from the protocol matter — and video is what reveals them. A report describing poor performance frequently sits alongside footage showing something considerably better, or showing that instructions were given incorrectly.
Note also that conditions can affect results such as an existing injury or a chronic condition are relevant and should be raised with counsel early, since they bear directly on the weight the testing carries.
The Video Requirement That Sets South Carolina Apart
South Carolina requires by statute that the incident be recorded — both at the roadside and in the breath testing room — and specifies what the recording must capture.
The roadside recording must generally begin when the officer activates emergency lights and must include the field sobriety testing and the advisement of rights. The breath testing recording must cover the entire testing process, including the observation period preceding the sample.
The consequences of non-compliance are real. Where the required recording was not made, or does not show what the statute requires, the prosecution’s case can be substantially weakened and in some circumstances dismissed. This makes obtaining and scrutinising the video the first substantive step in any South Carolina case — and it is why evidence needed for dui convictions in that state differs meaningfully from neighbouring jurisdictions.
Chemical Testing
Breath testing depends on a chain of technical requirements: the instrument must be an approved model, certified and maintained with records to prove it; the operator must hold current qualification; and an observation period — commonly around twenty minutes — must precede the sample to exclude mouth alcohol from belching, reflux or recent consumption. A break in that observation is a recognised basis for challenge.
Blood testing turns on who drew the sample and whether they were qualified, whether correct preservative and anticoagulant tubes were used, how the sample was stored and transported, and whether the chain of custody is documented. Improperly stored samples can undergo changes that affect the result.
Timing matters in every case. The reading reflects the moment of testing, not the moment of driving. Where consumption was recent, alcohol may still have been absorbing and the concentration while driving may have been lower — a technical argument requiring expert support rather than assertion.
Refusal carries its own consequences. Under implied consent provisions, declining a test typically triggers an administrative licence suspension independent of the criminal case, and the refusal itself may be admissible.
Prior Offences and Escalating Penalties
Penalties increase sharply with prior convictions, and states define the lookback period differently — a prior may count for a decade or longer depending on the jurisdiction.
Beyond fines and custody, the consequences that persist include licence suspension, ignition interlock requirements — which South Carolina has extended broadly, including to first convictions — mandatory alcohol education or treatment programmes, substantially increased insurance costs, and a criminal record affecting employment and professional licensing.
Where a collision caused serious injury or death, the offence escalates to a felony with materially greater exposure. And for non-citizens, any conviction warrants specific immigration advice alongside the criminal defence.
Frequently Asked Questions
Can I be convicted without a breath reading?
Yes. The impairment offence can be proved through driving behaviour, officer observations, field sobriety performance and video, without any chemical result.
Do I have to perform field sobriety tests?
In most states these are voluntary, though declining may itself be noted and does not prevent arrest. The consequences of refusing a chemical test are different and more serious.
What if there is no video?
In South Carolina the recording requirement is statutory, and non-compliance can significantly undermine the prosecution. Obtaining and reviewing the footage is the first step in any defence.
Can a medical condition explain my test performance?
Frequently. Inner ear disorders, neurological conditions, injuries, certain medications and even some diets can affect either the physical tests or the breath result. Raise these with counsel immediately.
Is my licence suspended straight away?
Administrative suspension commonly begins before the criminal case is resolved, particularly on refusal, and has its own short window for challenge. Deal with that deadline first.
Does the reading itself set the penalty?
In states using tiered structures, yes — penalties step up across concentration bands rather than applying uniformly above the threshold.
Understand the Elements
A prosecution has to establish operation, impairment or a prohibited concentration, and — in South Carolina — compliance with the statutory recording requirement. Each element rests on procedure that can be examined: the lawfulness of the stop, the administration of the tests, the certification of the instrument, the observation period, and the timing of the sample relative to driving. Obtaining the video and the maintenance records is where a defence actually begins.
This article is general information about criminal procedure and is not legal advice. Thresholds, offence structures, recording requirements and penalties vary by state and change — consult a qualified local attorney.
Related reading: Protecting Your Rights After a Phoenix Auto Accident.
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