Yes I agree that not taking drugs will ensure you dont fail a...

Yes I agree that not taking drugs will ensure you dont fail a drug test. But testing positive to a roadside drug test will not, in many cases indicate that you are driving while drug impaired, because there is no actual data to verify this (apart from some in vitro lab tests paid for by drug test manufaturers). Therefore, roadside drug testing may reduce some drug usage (by responsible drug users), but will not increase road safety, which is the whole purpose (and spin) for bringing in roadside testing. Don't do drugs.