More than 1,300 drivers agreed to provide breath or saliva samples at road stops in nine different California cities.
The Office of Traffic Safety says more than 14-percent tested positive for drugs, a little more than 7-percent tested positive for alcohol.
While marijuana was the most common, drivers also tested positive for prescription and over-the-counter medications that can impair driving.
The Office's Chris Cochran.
COCHRAN: "We know that alcohol, drunk-driving statistics have been going down, now this and other studies are showing that drugged driving is going up so we need to worry about that and educate the driving public and others about the problem."