A saliva test is decently accurate as a first pass to detect smoking in the past 48 hours or so. A blood test is more accurate, but can have 'positive' result for chronic smokers even if they've not smoked for weeks or months.
The problem is rather that unlike alcohol, 1) there's no matter of degrees and the cut-off point for testing 'positive' is extremely low, plus the punishment is unusually high, especially when compared to alcohol which provably impairs driving significantly (and almost certainly more severely than weed). And 2), contrary to all other drugs, the 'evidence' of smoking is stored in your body's fat, which means you can test positive even if you've not smoked in a long time (and are almost certainly not driving-impaired).
A saliva test is decently accurate as a first pass to detect smoking in the past 48 hours or so. A blood test is more accurate, but can have 'positive' result for chronic smokers even if they've not smoked for weeks or months.
The problem is rather that unlike alcohol, 1) there's no matter of degrees and the cut-off point for testing 'positive' is extremely low, plus the punishment is unusually high, especially when compared to alcohol which provably impairs driving significantly (and almost certainly more severely than weed). And 2), contrary to all other drugs, the 'evidence' of smoking is stored in your body's fat, which means you can test positive even if you've not smoked in a long time (and are almost certainly not driving-impaired).