If alcohol testing were like marijuana testing, almost every accident would be counted as a DUI. Because of the underlying chemistry involved, most statistics

If alcohol testing were like marijuana testing, almost every accident would be counted as a DUI. Because of the underlying chemistry involved, most statistics involving marijuana-related incidents vastly overstate instances of drugged driving, use, etc. This includes not just DUIs, but also numbers like the DAWN reports. Unlike almost any other drug, marijuana stays detectable in the system for 2 weeks on a test (for urine tests, which are the most common - in general, anywhere from 2 days to 3 months, depending on the type of test + usage habits). Since the effects of the drug only last for ~2-4 hours, that means that "testing positive" for marijuana is useless at indicating whether the person is actually under the influence, or just happened to use the drug at some point within the last two weeks. Contrast to most drugs - alcohol, for example, can only be detected for about as long as the person is impaired.