r.j. r r.j. reynoldsee more drivers participating in getting high and getting behind the wheel. >> some run humorous ads to get marijuana users to think before they get behind the wheel. >> colorado asked motorists to report reckless drivers. with alcohol, you can use a breath test to see how drunk someone is, but there's no comparable measurement for marijuana. a blood test would show marijuana use. >> we may have to take an individual to a hospital or other medical facility for that. >> but a sober person might test positive for marijuana because it can stay in your blood for a week. colorado's troopers brought in drug recognition experts. don says he has been trained to understand marijuana's effects on people. >> you might see their eyelids have tremors or their actual body has tremors. bloodshot watery eyes. >> this car blew through a stop sign. the trooper then smelled alcohol. >> did you have anything to drink while you were there? >> a couple hours ago. >> what did you have? a whiskey? >> yeah. >>