Traffic Law

Drive Under the Influence of Alcohol - DUI

Driving under the influence of alcohol, commonly referred to as DUI (NSW) is considered a major traffic offence. Unlike many other drink driving (such as PCA) offences, to prove a DUI offence, the police are not required to prove a blood-alcohol content or rely on a scientific device.

Like almost all drink driving offences, a conviction for a DUI offence means fines and automatic licence disqualification periods. It is therefore important to seek the advice of experienced traffic lawyer if charged with this type of offence. 

The Law

Pursuant to section 112 of the Road Transport Act 2013, A person must not, while under the influence of alcohol:

(a) drive a vehicle, or

(b) occupy the driving seat of a vehicle and attempt to put the vehicle in motion, or

(c) if the person is the holder of an applicable driver licence (other than an applicable provisional licence or applicable learner licence)-occupy the seat in or on a motor vehicle next to a learner driver who is driving the vehicle.


The penalties for a charge of DUI (NSW) or drive under the influence of alcohol are set out in the below table:


Maximum Fine


Minimum Interlock Period

Maximum Gaol







1st offence


12 months

6 months


9 months







2 or more


6 months

9 months

24 months

12 months

It is also an offence if the person is the holder of an applicable driver's licence and, whilst under the influence of alcohol, occupies the seat of a vehicle next to a learner driver who is driving the vehicle.

The maximum penalty under these circumstances is a fine of $2,200, whether a first or second offence, and there is no term of imprisonment. The disqualification periods are the same as in the table.

Mandatory Interlock

Since February 2015, a Court must make a Mandatory Interlock order upon convicting someone for their "second or subsequent" Drive Under the Influence of Alcohol (DUI) offence. An Interlock order requires an initial period of disqualification for anywhere between 6 and 9 months. After that period, the offender will need to obtain an Interlock licence should they wish to return to the road. This licence is to be held for as long as the Court orders, which is at least for the minimum period listed in the above table.

Read here for more on Mandatory Interlock Orders.


So what does it mean to be "under the influence of alcohol"? The legislation does not define the term and in fact, at law, it is a little ambiguous. To prove the offence, the Court needs to determine whether someone is under the influence of alcohol based on the surrounding circumstances and importantly, witness observations of the driver.

For example, police may give evidence that the person's breath smelt of intoxicating liquor, their eyes were blood shot, their speech was slurred and they were unsteady on their feet. The law allows people to give an opinion as to whether in their view someone was intoxicated or not, yet it must be based on some sort of observation.

The degree of intoxication that is required to make out the offence is not abundantly clear. It is accepted, however, that there must be some sort of impairment of the driver, however, the law does not require that the driver be impaired to any significant or substantial degree. It would be enough to find that the driver's mental or physical faculties are affected by alcohol to the point that they are no longer "normal".

It is important to note that in New South Wales, there is no requirement for the prosecution to prove that the driver's proper control of the vehicle was affected to find the offence proved, although this type of evidence could assist the Court in determining whether the driver was under the influence.

Whether someone is "under the influence" or not is based on opinion and is a finding of fact that needs to be made by the Court.

If we have other more specific drink driving matters, such as PCA (prescribed concentration of alcohol) offences, where the police rely on blood-alcohol readings obtained by scientific instruments, then why does the offence provision of driving under the influence of alcohol still exist? What sort of scenario would one typically be expected to be charged with driving under the influence of alcohol?

Police would typically prefer this charge where a driver is involved in an accident, there is some evidence that the driver may be intoxicated and the police are unable to obtain a blood-alcohol reading in accordance with legislative provisions that would allow the police to rely on the reading obtained. The offence is not as common as the other drink driving offences and is typically relied on by police when they are unable to prove a more specific offence, such as Mid Range PCA or High Range PCA, which require admissible evidence of the driver's blood-alcohol reading to be made out.

It is also important to note that, under certain circumstances, the Court can accept evidence from witnesses other than police officers as lay opinion. In fact, despite their position, police officers are lay witnesses when it comes assessing someone’s sobriety and, like most people, have to draw on life experience to form an opinion as to whether or not someone is “under the influence”.

It must be borne in mind that being “under the influence” is an element of the offence and therefore, must still be proved beyond a reasonable doubt. There can be circumstances where prosecution evidence can fall just short of proving that a driver was under the influence, especially where there is no available evidence as to whether or not the driver had consumed alcohol at any time prior to driving.

Sometimes, where the police decide to just charge someone with driving under the influence rather than obtaining a blood-alcohol level and charging them with a more specific PCA drink driving offence, it can result in some unfairness. For some, when comparing the penalties for DUI against the other penalties for drink driving offences, it can mean a similar or more favourable outcome, should the person decide to plead "guilty". But where the unfairness may resultis if someone is assessed as being “under the influence” even when their blood alcohol level may well have been below the legal threshold for driving.  In other words, the person may have given a reading of below 0.05 if they had been subjected to a breath analysis (for example, they had only consumed a small amount of alcohol) but still be assessed as being under the influence of alcohol by (police) witnesses. Of course, this would be a subjective assessment made a witness that the accused person would then need to defend. 

Despite some unfairness that can present itself against a driver where police charge the driver with DUI rather than subject the driver to a breath analysis and obtain a blood-alcohol reading, it is also the case that if police do in fact obtain a breath analysis sample, they are then precluded from charging the driver with DUI.  This allows protections for drivers against police subjecting someone to a breath analysis and then charging them with DUI should the analysis either return a reading below the threshold or a reading for a drink driving offence that is less serious than DUI. This is an often overlooked provision in the Road Transport legislation, by police, prosecutors and defence lawyers alike but can prove very important in cases where police prefer one charge to the other as a "back-up" or, where there are issues with the evidence and therefore, police decide to charge in the alternative. Quite simply, it cannot be done.

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