> They also 'verify' in the sense that any driver can challenge and get a "better than road side" test back at the station under supervision (blood tests with saved samples for court challenges, etc).

Blood tests can not determine THC intoxication.

I'm not seeing the part where I said that.

DUI (in Australia) refers to "Driving under influence" and focuses on threshold detection rather than degree of impairment (although relying upon other studies that allege to correlate the two).

In the case of drug impairment, "better than roadside swabs" evidence for court challenges includes samples of urine, breath, hair, saliva or sweat.

Blood samples, rather than breath tests, are typically for alcohol.

Independent of roadside pass / fail on swabs for drug / alcohol levels Australian RTA can still ask drivers to complete an impairment test; assessing balance, coordination, and overall behaviour.

On challenge, this is something that can also be further assessed for court evidence; eg: are their perceptions of impairment because (various) medical conditions that cause slurred words, etc.