You're a dog chasing it's tail.  Any reasonable rational person does not consume alcohol and then choose to drive a car.  Any reasonable rational person does not consume cannabis and then choose to drive a car. Any reasonable rational person does not consume prescription drugs then choose to drive a car. Any and all people who choose differently are criminals. Period. DUI for ANY substance has been illegal for decades.  The new LEGAL cannabis industry does not affect this part of criminal justice system  at all.