Since marijuana legalization, highway fatalities in Colorado are at near-historic lows - https://www.freerepublic.com/focus/f-chat/3280359/posts
https://www.denverpost.com/2017/08/25/colorado-marijuana-traffic-fatalities/
The number of drivers involved in fatal crashes in Colorado who tested positive for marijuana has risen sharply each year since 2013, more than doubling in that time, federal and state data show.
https://www.denverpost.com/2018/02/20/colorado-traffic-deaths-2017/
Traffic deaths in Colorado reached highest number in more than a decade in 2017 while number fell slightly across U.S.