The graph at https://www.denverpost.com/2017/12/26/colorado-roadway-deaths-2017-2/ shows that Colorado traffic deaths have been rising since 2011 - three years before legalization.
So pot use in CO was declining from 2011 to 2014? We’ll have to see if there is an acceleration in the graph after 2014.
Traffic fatalities have also increased in Washington state since pot was legalized. They increased in states in the 1970s the decriminalized pot.
Only someone completely doesn't realize that more legal ways to get high will result in more negligent deaths. Drug legalization of any kind diminishes everyone's quality of life.