How to Deal With a Drink Driving Charge

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This article was written by Michelle Makela - Legal Practice Director

Michelle has over 15 years experience in the legal industry, working across commercial litigation, criminal law, family law and estate planning.  Michelle has been involved in all practice areas of the firm and in her personal practice has had experience in litigation at all levels (State and Federal Industrial Tribunals, the Supreme Court, Court of Appeal, the Federal Court, Federal...

How to Deal With a Drink Driving Charge


Drink driving is often considered to be a trivial matter. However, this is not the case. Drink driving, even for a first offender, will very likely result in the recording of a criminal conviction, a fine and a period of licence disqualification. For mid and high range offenders, a sentence of imprisonment is not out of range, depending on the circumstances in which the offence occurred.

There is a common perception in the community that a drink driving charge can never be successfully defended. Though most drink driving charges result in a plea of guilty, there are circumstances in which it may be possible to successfully defend such a charge.

What is a PCA Charge?

Many people refer to drink driving charges as “DUI”. Most drink driving charges are not DUI but in fact PCA. DUI stands for Driving Under the Influence of alcohol. To prove a DUI charge, police have to prove that you were actually “under the influence” of alcohol at the time that you drove your car. Police may cite any visible signs of intoxication, such as bloodshot eyes or erratic driving as “proof” of being under the influence. This can be difficult and subjective. There is no objective or scientific way of telling whether or not a person is under the influence of alcohol.

PCA stands for Prescribed Concentration of Alcohol. This allows the police to charge a person with drink driving if they have in their blood more than the PCA, regardless of whether the person is actually under the influence of alcohol. This makes it much easier for police to charge people, because it is usually easy to scientifically measure a person’s PCA with a great degree of precision. That said, there are still possible ways to defend a PCA charge.

Challenging the Reading

The machines which the police use to measure your PCA (alcoholmeters) are usually very accurate and well maintained. There is also a presumption that the readings given by breath analysis machines are reliable. As such, challenging the accuracy of the alcoholmeters is usually not easy. But it is sometimes possible to prove that the reading produced by the alcoholmeters is not the same as the reading you had at the time of driving.

It is important to remember that the offence is having a prescribed concentrate of alcohol in your system while you are driving. Therefore, it is the reading at the time you were driving that would be in question.

It normally takes about 30 minutes for the police to arrest you, take you back to the station (or mobile “booze bus”) and test your PCA accurately (the breath testing devices that you blow into at the side of the road are prone to error, so their reading is not enough to allow the police to charge you).

It is normal for your blood alcohol level to go up and down over time. As such, the reading recorded by the alcoholmeter may not be a good representation of your blood alcohol content at the time of driving.

Despite the fact that the reading produced by a breath analysis machine at the station is deemed accurate, there may be a way to challenge that reading. If your PCA is in question, your legal representative may wish to retain an expert to calculate your likely reading at the time of driving.

Pharmacologists are experts in how different drugs and substances interact with biological systems. They would be able to calculate a likely reading at the time of driving given the proper information, including:

  • number of drinks;
  • alcohol content of those drinks;
  • time period in which the drinks were consumed;
  • food consumed;
  • physical features, such as age, height, weight, body type; and
  • any medical issues or medication being taken.

In essence, it is sometimes possible to show that, although you were over the limit at the time of your breath analysis, you were not over the limit at the time you drove, hence you are not guilty of a PCA offence.

Further to that, even when you are over the limit, these same principles can sometimes be applied to reduce the range, for example from a high range to a mid range. This would substantially reduce the maximum penalties applicable. To determine if it is worthwhile to pursue this kind of defence we advise that you speak to an experienced legal practitioner. Likelihood of success would depend on factors including your reading, how much alcohol you drank, when you drank it and how much and what you ate on the day.

Honest and Reasonable Mistake

The law provides for a number of defences to drink driving charges. One of them is called the “honest and reasonable mistake of fact” defence (sometimes also called the Proudman and Dayman defence after the name of the case which established it).

This defence states that you are not guilty of a drink driving offence if, at the time of driving, you:

  • honestly believed that you were under the limit; and
  • in the opinion of the court, it was reasonable for you to hold that belief in all of the circumstances of your case.

How does this defence apply in practice?

In practice, this defence can be difficult to succeed on. Courts are very cautious to make sure that drink drivers do not get off charges just because they say that they did not think they were over the limit. Each case depends on its own particular circumstances but below are some general types of cases where this defence may be worth considering.

Morning after the night before

If you have been drinking the previous night, then went to bed and had a decent sleep and drove the following morning honestly thinking that all the alcohol that you consumed the previous night would have been eliminated from your system, a court may be prepared to accept that it was reasonable for you to do so. Of course, much depends on your actual reading, the number of hours since your last drink and how much you had to drink the previous night, but if you are in this category, it is worth speaking to a lawyer about the possibility of running this defence.

Relying of rule of thumb

Another case where this defence may apply is where you had relied on the rule of thumb which used to be taught by Roads and Maritime Services (now Transport for NSW) to learner drivers. Some years ago, RMS  publicised a rule of thumb which people could use to enjoy a drink but at the same time stay under the limit. This rule was:

  • For men – two standard drinks in the first hour and one each hour thereafter
  • For women – one standard drink an hour

This rule is no longer publicised because it has been shown to be inaccurate. However, many people still use it because that is the rule they were taught when studying for their “L” plates. Also, regrettably, there are still some pubs and clubs which display signs promoting this as a safe rule to follow.

If you have relied on this rule, and were meticulous to make sure that you stayed within it, then drove thinking that you must be under the limit, a court may be prepared to accept the defence of honest and reasonable mistake of fact.

Drink spiking

If you think that your reading may be as high as it was because your drink has been spiked, that is also a scenario in which this defence can be used.

These categories do not represent the only scenarios in which a defence of honest and reasonable mistake can be used to defend against a drink driving charge. To get the full picture it is very important to speak to a lawyer who is an expert in traffic law in order to determine whether this (or for that matter some other) defence is worth running in the particular circumstances of your case.

The Two Hour Rule

It is a little known fact that the police cannot rely on a breath test if it was taken over 2 hours since you last drove a car. What this means is that even if the police take a breath test from you, if it was taken more than 2 hours after you drove, that reading may not be able to be used for evidentiary purposes to prove that you were intoxicated.

Generally, police stay well within the two hour rule but there are times when the rule is breached. This is most common in situations where police attend at the scene of an accident. Not infrequently, by the time the police arrive at the scene, more than 2 hours has passed since the time of the accident.

The Home Safe Rule

Equally unknown is this rule, which states the police have no power to require you to submit to a breath test at your home. As with the two hour rule, if police breath test you in breach of that rule, the evidence of your reading may be thrown out of court.

The precise legal meaning of what is a person’s home is complex (for example, is the driveway of a block of units considered your home?). However, if you think you may have a possible defence on this basis, we suggest that you contact an experienced criminal lawyer.

For advice or representation in any legal matter, please contact Armstrong Legal.

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