How Did Marijuana Legalization Affect Washington DUI Law?

The effect of decriminalization of recreational marijuana use on Washington DUI law.

In November 2012, Washington voters legalized recreational marijuana use by passing “Initiative Measure No. 502” (more commonly known as “I-502”). I-502 not only decriminalized use and possession of small amounts of marijuana, it made changes to Washington DUI (driving under the influence) law.

Per Se and Impairment DUIs

Prior to the passage of I-502, a Washington motorist could be convicted of a DUI for driving while:

  • as the result of ingesting drugs or alcohol, “the person's ability to drive a motor vehicle is lessened in any appreciable degree," or
  • having a blood alcohol concentration (BAC) of .08% or greater (a “per se” DUI).

So, a driver could be convicted of a DUI for marijuana use only if the prosecution could prove the driver was “affected by” the use. Showing the driver’s blood had a high concentration of marijuana wouldn’t have been enough to get a conviction. (Read more about the two types of DUIs, see What’s the Difference Between Per Se and Impairment DUIs?)

I-502 Establishes the “Per Se Marijuana” DUI

I-502 added a third type of DUI to the books—a “per se marijuana” DUI. A motorist can be convicted of a per se marijuana DUI for driving with a concentration of five nanograms or more of THC (the primary psychoactive ingredient in marijuana) per milliliter blood. So with the new law, a marijuana DUI conviction can be based on impairment or THC concentration in the blood. (Wash. Rev. Code Ann. § § 46.61.502(1), 46.61.506(2) (2016).)

I-502 also added a provision that requires the Washington State Department of Licensing to impose an administrative license suspension for anyone caught driving with a THC concentration of five nanograms or more. Previously, administrative license suspensions were applicable to only alcohol-related DUI offenses where the driver’s BAC was at least .08%. (Wash. Rev. Code Ann. § 46.20.308(5) (2016).)

(Learn about the consequences of a Washington DUI conviction.)

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