Marijuana legalization complicates impaired driving assessments

MIAMI - AUGUST 11: A City of Miami police car with lights ablaze responds to a call as they patrol the street on August 11, 2010 in Miami, Florida. The Miami Police Department launched "Operation Take Back Our Streets" yesterday in response to recent shootings in the Model City and Little Haiti communities of Miami. The city has seen a number of shootings recently using high powered assault weapons. (Photo by Joe Raedle/Getty Images)