DUI per se laws, stricter law enforcement, education, and changing social norms have led to a steady decline in the incidence of drunk driving and drunk-driving deaths according to NHTSA:
But changing social norms and a lack of effective drug per se laws that have hindered law enforcement, have led to a dramatic increase in drugged driving. This chart shows the percentage of fatally injured drivers positive for drugs.
Patterns among Colorado drivers are similar to these national statsitics. From 2006 to 2010, the number of Colorado drivers involved in fatal crashes declined 17%. But the number of drivers involved in fatal crashes who tested positive for drugs increased 5% (CDOT/FARS). In 2011, 36% of Colorado drivers involved in fatal crashes for whom drug test results were available tested positive for at least one illicit drug (CDOT/FARS March, 2013).