Drink-driving prosecutions in NSW rely on strict procedures under the Road Transport Act 2013 (NSW). Police must follow these procedures precisely — from stopping the vehicle, to conducting breath analysis, to collecting and handling blood samples.

When these legal requirements are not met, the results may be flawed, unreliable, or inadmissible. Below are six key areas where drink-driving results can potentially be challenged.

1. Delays in Breath Analysis (“As Soon As Practicable”)

Under s.21 of the Road Transport Act, police must take a driver for breath analysis “as soon as practicable” after a positive roadside test.

Why this requirement exists

Alcohol rises and falls in the bloodstream over time. A delay between driving and breath analysis can mean the reading no longer reflects the BAC at the time of the alleged offence.

Delays that may raise legal issues

• waiting at the roadside longer than necessary
• long transport times that could have been avoided
• police conducting non-essential tasks before analysis
• extended waiting periods at the station before the test

If the delay was avoidable or unjustified, lawyers may argue the BAC was lower when the person was driving, affecting the accuracy of the charge.

2. Unlawful Stop, Detention, or Testing Request

Police powers to stop vehicles and conduct roadside tests come from s.148–151 of the Road Transport Act.

What the law allows

Police may stop any driver at any time to conduct a breath test — suspicion is not required.

Where problems arise

• detaining a driver longer than needed after a negative roadside test
• stopping a vehicle that is not on a road or “road-related area”
• issuing a breath analysis direction without a lawful basis
• continuing detention after the driver has complied with all requirements

If the stop or detention itself was unlawful, anything that follows — including the breath analysis reading — may be challenged as evidence obtained outside lawful powers.

3. Issues with the Approved Breath Analysis Instrument

A breath analysis reading is only admissible if taken using an approved instrument under the Road Transport Act. The device must be part of the NSW-approved list and maintained by NSW Police according to operational standards.

Grounds for challenge include:

• the machine was not listed as an “approved instrument” at the time
• calibration records are missing or out of date
• known faults or error messages during the test
• low breath volume not properly accounted for
• the operator was not trained or authorised to use the machine

Because breath analysis is scientific evidence, even small inconsistencies can undermine confidence in the reading.

4. Blood Sample Errors: Chain of Custody & Authorisation

Blood samples taken under s.24–25 require strict compliance with procedure.

Samples may be contestable if:

• the sample was not taken by an authorised medical practitioner or nurse
• packaging seals were broken or improperly applied
• labels were incomplete, incorrect, or missing identifying details
• transport or storage conditions breached NSW Health procedure
• chain-of-custody documentation is missing or inconsistent

Any break in the chain raises doubt about whether the sample remained intact and untampered from collection to laboratory analysis.

5. Medical or Physiological Factors Affecting Breath Test Reliability

Police must follow procedural standards during breath testing (NSW Police RBT Program). Certain conditions may interfere with the accuracy of breath analysis:

Examples include:

• respiratory conditions limiting ability to blow steadily
• recent vomiting or regurgitation, leaving alcohol residue in the mouth
• GERD or reflux, which can cause “mouth alcohol”
• dental work or retainers holding traces of alcohol
• medications containing ethanol (if not accounted for)

NSW Police are required to observe the person before analysis. If they did not allow proper observation time or failed to assess medical limitations, the reading may be open to challenge.

6. Timing-Based Arguments (“Rising BAC”), Delay, and Metabolism

Even when police act lawfully, timing can still be an issue. After a person stops drinking, their BAC may continue rising for 30–60 minutes. If a breath analysis is delayed — even lawfully — the reading at the station may be higher than at the time of driving.

A valid rising-BAC challenge generally requires:

• evidence of when the person last consumed alcohol
• analysis of whether police complied with s.21 timing requirements
• toxicology interpretation (absorption/metabolism curve)

This defence does not dispute the reading itself, but whether it accurately represents the BAC at the time of driving — the key requirement for a PCA offence.

Need Advice on Challenging a Drink-Driving Result?

If you believe your breath or blood test was not conducted correctly, or if you’re unsure whether police followed the required legal steps, getting the right advice early can make a significant difference to your case.

Ly Lawyers can review the evidence, identify any procedural errors under the Road Transport Act, and advise you on the strongest path forward — whether that’s negotiating, reducing penalties, or challenging the results entirely.

Contact Ly Lawyers today for immediate, experienced representation in all drink-driving matters.