The Washington State laws and regulations have been changing rapidly as our legislators attempt to work out a better state regulated marijuana retail industry. Marijuana DUI limits have been difficult to define because each strain has its own unique profile of effects and potency; people are also effected differently to a substantial degree depending on frequency of use.
In 2013, CNN released a report they had compiled on the impairment of drivers after smoking marijuana. CNN had several drivers smoke marijuana until they were above the current marijuana DUI limit of 5ng of THC per mililiter of blood; they were then subjected to a driving test.
According to CNN:
[The real start of the experiment was having each of the participants smoke three-tenths of a gram of herb. After that, blood tests showed that all three were well over the limit. Dylan and Jeff came in at 26 nanograms and 22 nanograms respectively. Abbey was the highest in more ways than one, coming in at 36.7 nanograms of THC per milliliter of blood.]
Using the CNN report for our basis in logic, we can deduce that smoking a single bowl of marijuana will put you at THC levels well in excess of the current driving limits… Please smoke responsibly and don’t drive if you’re high!
Source: CNN high driving test shows five nanogram limit much too low.