that part is the tough part. i also believe it would fall under the same parameters it does now. there is no real ''test'' to find out if someone is under the influence of marijuana, however a series of field tests and judgement call by the officer is usually how it goes, and probably would go. there is a saliva test but it would prove inaccurate because thc in your saliva lasts for 12 hours at the least.
either way id like to think that a few field tests, checking for dilation of the pupils would still be used.
thanks squirrel i knew it was spelled wrong when i typed it. couldnt find the correct spelling.