WATCH: How can police tell if you are too high for the highway?

LOS ANGELES, CA - How can officers tell if drivers are too high for the highway? We all know when it comes to alcohol consumption, the more there is in your blood stream, the worse off you are. But it's not so simple when it comes to 'The Devils Lettuce'.

A new study by the AAA's Safety Foundation says some drivers can have low levels of THC in their blood streams and still be impaired behind the wheel. While others with high levels of THC may not be as dangerous or even feel the effects of it. This is because marijuana is not metabolized the same way as alcohol.

Currently six states use blood level tests to determine if a driver is impaired. Now that may not be the best way to figure out if someone is unfit to drive.

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