Actually, no, there aren’t. As of this moment, there’s no way to know if you’re intoxicated by marijuana, and, since that’s legal in a number of US states, that’s a ‘problem’. (Although, let’s be real, stoned people tend to drive reeeeeeaaaaaalllllllllly slowly, not exactly hugely dangerous.) You can detect the metabolites with a urine or blood test, but that doesn’t tell you how long ago you used it, or if you’re still under the influence.