Key findings:

The prevalence of drug driving among PWID remained high across 2006-2011, whilst the frequency dropped more than threefold to a median of 24 occasions in a six month period (once a week).
There were few significant predictors of drug driving. A higher frequency of heroin use, and having completed any courses after school, were positively associated with drug driving; whilst those who had recently suffered from drug induced psychosis were less likely to have engaged in drug driving.
The use of cannabis prior to the last drug driving occasion decreased significantly from 2007-2011, whilst in 2011 the use of heroin increased.
There was a downward trend in the use of all pharmaceutical drugs prior to driving, with significant declines observed for morphine, methadone and subutex.
Across 2007-2011 the majority of drug drivers continued to report that the use of drugs prior to driving had no impact upon their driving ability. Participants who had used methamphetamine prior to driving were more likely to believe that this had improved their ability to drive, whilst those who had used heroin and subutex were more likely to report that their driving ability had impaired by the use of such drugs.
Drink driving was comparatively low among PWID, with less than 10% of recent drivers reporting that they had driven whilst over legal blood alcohol concentration limit. Younger participants, and those that were male, were more likely to have engaged in drink driving.

Citation: Sutherland, R and Burns, L. (2011). Driving behaviours among people who inject drugs in South Australia, 2006-2011. Drug Trends Bulletin, December 2011. Sydney: National Drug and Alcohol Research Centre, University of New South Wales.