Fatal accidents involving stoned drivers have soared in the state of Washington since marijuana was legalized there, according to a study from the AAA Foundation for Traffic Safety. But it’s difficult to determine whether a high-on-pot driver is too impaired to drive, according to a separate study from the same group. Fatal crashes involving drivers who recently used marijuana more than doubled in 2014. Pot was involved in 17% of fatal crashes in Washington in 2014, up from 8% in 2013 -- the year before recreational marijuana was allowed there.