A survey of California drivers finds they are almost twice as likely to test positive for drugs that may impair driving, compared with alcohol. The Los Angeles Times reports 7.3 percent of drivers tested positive for alcohol, compared with 14 percent who tested positive for impairing drugs, including both illegal and prescription drugs.

Of those who tested positive for alcohol, 23 percent also did so for at least one other drug, the survey found. Marijuana was the most common drug found in the system of drivers. More than one-quarter of drivers who tested positive for marijuana also tested positive for at least one other drug.

The survey, conducted by the California Office of Traffic Safety, included 1,300 drivers who voluntarily provided breath and/or saliva samples at roadside stops on weekend evenings.

“These results reinforce our belief that driving after consuming potentially impairing drugs is a serious and growing problem,” Christopher J. Murphy, Director of the Office of Traffic Safety, said in a statement.