It is an offence to drive a vehicle, or attempt to put a vehicle in motion, while so much under the influence of alcohol or a drug as to be incapable of exercising effective control of the vehicle [Road Traffic Act 1961 (SA) s 47].

This offence applies to all vehicles rather than just motor vehicles. This includes trams, bicycles, animals (such as a horse), animal-drawn vehicles and motorised wheelchairs that can travel over 10 kilometres per hour [s 5]. From 13 July 2025 it also includes e-scooters and other personal mobility devices.

The charge of driving under the influence is not the same as driving with the prescribed concentration of alcohol and it is possible to be convicted of driving under the influence of alcohol even if the blood alcohol level is less than the prescribed concentration. For the purposes of this offence, a person is deemed to be incapable of exercising effective control of a vehicle if any physical or mental faculty is lost or appreciably impaired [s 47(2)].

The prosecution may be able to prove a charge of driving under the influence with evidence of the manner in which the vehicle was being driven and of signs of intoxication (including observations by the police and other witnesses), the smell of alcohol about the driver, unsteadiness, watery or bloodshot eyes and slow or slurred speech.

For the penalties, see alcohol and drug penalties.