Ann: Half Year Accounts, page-227

You can take offense all you like. Until testing has an accurate methodology to gauge what 0.05 looks like for any of those drugs, I'd rather a ZERO tolerance policy tha what you're suggesting. There is no current testing protocol that accurately tells you if usage is recent vs non recent, as THC (as you should well know) is stored in fat and has different release mechanisms based on occasional/heavy usage, tolerance etc. Alcohol is a fairly clear cut test, your blood alcohol limit doesn't determine your impairedness, but rather a physical quantity in the blood. That physical quantity can then be judged against the population mean for safety and a law applied.

Without that clear cut testing approach, I'd rather air on the side of caution than letting impaired drivers kill innocents for no real purpose (and no, getting high is not a purpose).