The point I'm making nihilism is that they need to do thorough...

The point I'm making nihilism is that they need to do thorough testing including those that have higher tolerances to the THC in marijuana if they are going to do anything comparative to alcohol testing.
As previous, I doubt there would be much difference between someone driving high on marijuana for the first time & elderly drivers who drive very slowly.
Current research is mostly based on accidents where there are "other" contributing factors like alcohol & speed are involved with the marijuana. We need to see driver reflex testing based on marijuana only (then taken in conjunction with alcohol etc.) including drivers of different tolerances if we are to get more qualified research on the subject & make better informed decisions, especially if we are looking at legalising in the near future.