The passage of Initiative 502 sets a legal limit of five nanograms of THC, marijuana's active ingredient, per milliliter of blood for drivers over 21.
Bellingham DUI attorney Jonathan Rands says that level is "shockingly" low, and there is no research showing that level causes impairment.
THC stays in a user's system for a long time, and Rands says regular pot users are likely to always be above the legal limit even when they're not stoned.
The law says drivers under 21 cannot be found with any level of THC in their blood.
Rands says that means young drivers could be accused of stoned driving for days or weeks after their last time using marijuana.