News · Criminal law explainer
DUI versus PCA in NSW.
People use drink driving and DUI as if they mean the same thing, but in New South Wales they are different offences. One is about your reading, the other about your actual impairment. This note explains the difference between a PCA offence and driving under the influence, how each is proved, and why it matters.
By Aaron Kernaghan · Published 3 September 2026
A PCA offence, prescribed concentration of alcohol, is based on your blood or breath alcohol reading being over a limit, and does not require proof that you were actually impaired. Driving under the influence (DUI) is based on your driving being actually affected by alcohol or a drug, and does not depend on a reading. They are separate offences, and DUI is often used where there is no reliable reading, such as with drugs.
What is a PCA offence?
PCA stands for prescribed concentration of alcohol. A PCA offence is committed where a person drives with a blood or breath alcohol concentration at or above the limit for their licence and range, proved by a breath analysis or blood test. The ranges run from novice and special, through low, mid, and high range.
A PCA offence does not require proof that the person was actually affected by the alcohol. The reading itself proves the offence. That is why it is the most common drink-driving charge; the reading does the work.
What is driving under the influence?
Driving under the influence, or DUI, is committed where a person drives while actually under the influence of alcohol or a drug, to the point that their driving is affected. It does not depend on a specific reading. It is proved by evidence of impairment, such as the manner of driving, observations of the driver, and admissions.
DUI is often used where a reading is not available or not reliable, for example where the driver was affected by drugs, or where a breath analysis could not be obtained. It captures impairment directly.
How is each proved?
A PCA offence is proved by the reading from an approved breath analysis or a blood test, taken within the time the law allows, together with evidence the person was driving. The certificate of the analysis is central. DUI is proved by evidence that the person was affected: driving behaviour, physical signs, field observations, and any drug or alcohol evidence.
So a PCA case is often about the reading and its validity, while a DUI case is about the evidence of impairment. The defences differ accordingly.
Why the difference matters
The distinction matters because it changes what the prosecution must prove and where the case can be challenged. A PCA charge can be defended on the validity of the reading, the timing of the test, or whether the person was driving. A DUI charge can be defended on whether the driving was actually affected.
It also matters for drugs. Because there is no equivalent reading for many drugs in the same way as alcohol, DUI, alongside the presence-based drug driving offences, is how drug-affected driving is often prosecuted.
What are the penalties?
Both PCA and DUI are criminal offences carrying fines, disqualification, and a possible criminal record, and for most of them the mandatory interlock program applies. The penalties depend on the seriousness and the person's history, as with other drink-driving offences.
Whichever offence is charged, the outcome depends on the facts and how the matter is run. Our notes on PCA offences and breath tests and first offenders explain the consequences.
Frequently asked.
What is the difference between DUI and PCA in NSW?
A PCA offence is based on your blood or breath alcohol reading being over the limit and does not require proof of impairment. DUI is based on your driving being actually affected by alcohol or a drug and does not depend on a reading.
What is a PCA offence?
Driving with a prescribed concentration of alcohol, meaning a blood or breath alcohol reading at or above the limit for your licence and range, proved by a breath analysis or blood test.
What is driving under the influence?
Driving while actually under the influence of alcohol or a drug so that your driving is affected. It is proved by evidence of impairment, not a specific reading, and is often used for drug-affected driving.
Why does the difference matter?
It changes what the prosecution must prove. A PCA charge turns on the reading and its validity; a DUI charge turns on evidence of actual impairment. The available defences differ accordingly.
Are DUI and PCA both criminal offences?
Yes. Both carry fines, disqualification, and a possible criminal record, and for most of them the mandatory alcohol interlock program applies. The penalties depend on the seriousness and the person's history.
To speak to a criminal defence lawyer, call Aaron Kernaghan on 0421 717 019.
This article is written by Aaron Kernaghan, criminal defence lawyer at Good Legal Lawyers, as at 3 September 2026. It is commentary and reflects the personal opinion of the author only. It is not legal advice, it is not a substitute for advice on your own matter, and it does not purport to be accurate or complete. Any matter referred to may be before the court and any person charged is presumed innocent. For advice on a specific matter, contact Aaron Kernaghan on 0421 717 019 or contact the firm.
More criminal-law commentary by Aaron Kernaghan.
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