Very simple question. If the "number drivers involved in fatal crashes in Colorado who tested positive for marijuana" has doubles since 2013, why has Colorado's Highway Fatality rate remained constant for more than a decade?  The very chart used to show rise in fatalities  (https://www.codot.gov/news/documents/safety-press-conference-boards-jan-31-2017) showed a  remarkably stable fatality rate of about 5.8 MVM ( No Units listed). 
Its notable that Colorado's fatality rate is among the lowest in the nation about is about 1/2 the rate of NM(11.1), 1/3 the rate of Miss(16.0), and about 1/4 the rate of Nebraska(20.2).

Studies show that the rate of Cannabis use has almost doubled in past decade, while the fatality rate has essentially remained constant.  This can ONLY be true if Cannabis use has little effect on the Fatality Rate.  Focus on pills and booze.