In Colorado they don't have time to drink and drive because they stay home and get stoned.

According to a study done by both the University of Colorado and Montana State University found that traffic-death rates drop by nearly 9% in states after they legalize marijuana for medical use.  Variables like changes in traffic laws, seat-belt usage and miles driven were taken into account.

The researchers believe the difference is due to young people spending more time smoking and less time drinking.  A 12% drop in alcohol-related fatal-crash rates and a 19% drop in the fatality rate of people in their 20's was also observed.

For more see this source article.