they have junk they can drink/take for a couple a days and pee clean. it'd take a few off the road but not many..
An couple of weeks ago an friend got pulled over by the cops, he had drank 6 beers and after that he took 3 extacy pills (over an period of time that evening), the cops notice that he was intoxicated (drunk) and starts to search him.
After that they drive him to police station (while my friend pops his 4th extacy pill, wich was hidden in his sock).
And guess what, the computer based alco test machine gives an reading of 0,001, it says that hes sober, the police men then politly gives him an ride back to his car and he drives away...
Lucky guy!