I found this of interest
To all potheads who actually think that they can drive: basically if you can't spend 8 hours without taking drugs, we don't want you on the road. simple, not complicated at all...move along everyone this question is finally solved.
to all cannabis users: remember that all alcoholics think they are perfectly fine to drive
here what is REALLY scary:
Among marijuana users in the survey, 28 per cent had reported driving under the influence at some point, and among that group, 25 per cent felt it was less dangerous than driving drunk and 17 per cent felt there was no risk to their driving. (wow, just wow, and that is why education is needed)
39 per cent of marijuana users had at some point driven within two hours of consuming cannabis, and only half of pot users felt the drug affected their driving ability. (take a taxi, call your mom, don't drive!)
“One of the worst things that we did with alcohol many, many years ago was set a limit, because it gets people to ask the wrong question,” he said. “It’s ‘how much can I have and still drive?’ It leads to a guessing game, and people guess wrong.”
The new per se limits on THC would allow police to immediately lay charges based on the blood test results.
But the saliva-testing machines will stop detecting it after six to eight hours, so that’s the only safe answer.
https://ottawacitizen.com/news/politics/how-much-cannabis-is-safe-to-consume-before-driving-nobody-knows-but-were-setting-legal-limits-anyway/wcm/d007fd5a-715f-4f1c-a0f4-d3c4e2008753