Critics protested the proposed new limit for THC in the blood last year. They said it would ensnare good, responsible drivers and slap them with DUIs they didn't deserve. They said pot makes people drive better. Seattlepi.com reports:

A Buckley man accused of running over a teen as he walked hand-in-hand with his girlfriend has been charged with vehicular homicide.

King County prosecutors contend Cody R. Money was high on marijuana and prescription painkillers when he drove into 16-year-old Justin Relethford on Halloween. Money, 20, is alleged to have had a blood-marijuana level nearly twice the legal limit hours after the fatal crash. ...

Money tested positive for oxycodone – a prescription pain medication – as well as marijuana during a blood draw conducted three hours after the crash, the detective told the court. Money is alleged to have registered an active THC level of 9.5, nearly double the 5 nanograms-per-milliliter standard set under the state’s marijuana decriminalization law.

This incident—this horrible tragedy, which also involved a cell phone and painkillers—occurred before Initiative 502 passed, thereby establishing a limit for THC in the blood, but that limit is there just for reasons like this: to remind people that you shouldn't drive stoned (on painkillers or pot). Still, it seems the defendant isn't even charged with DUI.