San Francisco Chronicle
By Peter Fimrite

There are certain telltale signs that a person is stoned: bloodshot eyes, forgetfulness, ravenous late-night cravings.

But the November ballot measure that would legalize recreational pot in California says nothing about how police should detect tokers who climb behind the wheel. There’s no marijuana equivalent to the famed blood-alcohol content tests — taken by breath, blood or urine — that have planted .08 into the American consciousness.

It’s not a pressing concern for marijuana advocates, even as entrepreneurs try to develop a better sobriety test for dope smokers. But it’s a big quandary for California law enforcement officers, who are facing a question that has vexed several other states where recreational pot is legal.

California law bars driving under the influence of psychoactive substances, including weed. But with no definitive measurement for intoxication, arrests are often challenged, with officers relying on evidence like indecisiveness behind the wheel or a pungent car interior.