If Colorado or Washington police pull you over and find more than 5 nanograms of the mind-altering ingredient of marijuana per milliliter of blood in your system, you’re guilty of stoned driving – whether you smoked three days ago or three hours ago.

And you could lose your license.

Not so in Oregon. In this state, so far at least, there’s no established limit for the amount of THC, the psychoactive ingredient in marijuana, you can have in your blood before you are presumed to be impaired while driving.

Consuming and possessing pot is allowed in all three states. The science is lacking, though, when it comes to how to keep consumers and other drivers safe on the road. The THC-limit laws some states have adopted are arbitrary. And even if people could agree on a pot equivalent to the .08 blood alcohol content threshold used for drunken driving, no breathalyzer-type device exists when it comes to marijuana.

But the race is on for companies trying to create a test that can judge impairment. [Read more at the Portland Oregonian]