Per T:
They don't
need a test for pot to bust intoxicated drivers. Just
follow the guy and put his driving on your dash cam,
show it in court, and busted ...

This is totally tangential... but yesterday I heard a standup comedian
do a spiel on why drunk driving criteria based on the same blood alcohol
level for everybody are unfair.

Paraphrasing:

"I'm driving along and a cop pulls me over".

"Have you been drinking?"

"Well, I had five beers..."

"Please show me your driver's licence and registration."

"Oh... your name is Madigan!... You could have had 8. Have a nice day."
--
Pete Cresswell