The hazards of drunken driving are well known, and a new research review shows that adding pot to the mix only makes matters worse. The analysis of 57 past studies found that the combination of alcohol and marijuana compromised people’s driving skills to a greater degree than either substance alone. And while alcohol was more impairing, marijuana was not as benign as some believe. The findings — published online Jan. 26 in the journal Addiction — come at a time when a growing number of people may be driving with THC in their system.