The difficulty with per se testing is that drugs affect everybody differently, so it's not going to be possible, at least from my understanding having talked to the experts, to say that everyone will be impaired at a particular level. The only answer to that, unless there is some science that evolves to deal with that, is to perhaps have a sample or substance and some sort of other testing in conjunction with that. The only other option is to remain with the drug recognition experts.
On September 18th, 2017. See this statement in context.