What is the legislation in regard to cannabis use and drug driving?

It is illegal to drive under the influence of illicit drugs (including cannabis) in Australia.  Driving under the influence of cannabis carries penalties including disqualification from driving, demerit points, heavy fines, and/or imprisonment. The penalties imposed vary from state to state, and whether the offender is committing their first or subsequent drug driving offence. 

In all Australian jurisdictions, legislation has been passed that allows for roadside saliva testing for drug driving, including tests for cannabis.