The blood alcohol content that triggers a drink driving offence depends upon several factors. Drivers commit an offence if they drive while under the influence of alcohol, but it is not necessary to be drunk or impaired by alcohol to be charged with a drink driving offence.
Driving with a blood alcohol content (BAC) that exceeds a specified limit is also an offence. Since that offence can have serious consequences, you should talk to a lawyer if you are accused of driving while you are “over the limit.”
Your blood alcohol content is a measurement of the number of grams of alcohol in 100 mL of your blood. It can be accurately measured by a blood test. It is more commonly measured by a breath test using a device that samples deep lung air and uses a formula to convert alcohol detected in your breath to alcohol in your blood. Since that formula depends upon assumptions that are not necessarily true in every case, a breath test is less accurate than a blood test.
It is an offence in Western Australia to drive if your BAC is 0.05 or higher. That limit applies to adult drivers who hold a full licence and are driving ordinary vehicles for their own transportation.
A driver who has held a licence for less than two years cannot legally drive with a BAC above zero. A P-plate driver who has been licenced for more than two years is subject to the same 0.05 limit as other drivers.
Drivers cannot legally drive with a BAC above zero when:
Driving a vehicle while carrying any passengers if the vehicle is designed to carry at least 11 passengers;
Driving an omnibus while carrying passengers for hire;
If you are subject to a BAC limit of zero, you face a more serious penalty if your BAC is 0.02 or higher. If it is 0.05 or higher, you will be charged with the same drink driving offence that applies to all drivers. That offence also carries more severe penalties.
As BAC levels increase, so do penalties. The highest penalties generally apply to drivers who have a BAC of 0.15 or higher. You should talk to a lawyer whenever you are accused of driving with a prohibited BAC.