It doesn't matter if ur high, it matters if thc is detected....there is no mental status or sobriety test to determine to a legal standard..."highness", its a biologic or physiologic assay that you are prosecuted with....its really not if you are high or not, though if you are acting "high" it will give them "reasonable cause to stop you, do an investigation and determine if you are high...by doing an in mouth or serum assay. Perhaps I'm jaded, but now they can perhaps impound your car, fine you up your ass, loose a professional license, and perhaps confiscate your property and wages.
the thc test will be analogous to the breathalyzer. they can't just stop people and test them because they feel like it or just for fun (in theory). they still need some kind of probable cause - the car smelling like weed, weaving thru traffic, a bong on your dashboard, grandpa cheech riding shotgun and taking shotguns, etc.
i'm also not really trying to advocate anything in particular here - just trying to clear up some details....