"Roadside saliva testing for drugs already takes place in Australia and Germany"
-- I agree with this, this really should be done to minimize cases like this, i have a friend who's a victim too of drink and drugs influenced people whos still driving.
In our company where i work they do test us for drink and drugs. I have one gadget too, most of us actually to test our alcohol level, its a personal breathalyser that we usually bring whenever we drive to office or wherever to go. Its important to have one and so far accurate.