There are several reasons why drunk driving is easier to police than drugged driving. The impact of alcohol on a person's ability to drive is comparatively predictable. It is easier to test for the presence of alcohol than other drugs. The signs of impairment are easier for law enforcement officers to identify. While drunk driving involves one substance, alcohol, drugged driving must cover a range of substances, both legal and illegal, each of which carries its own concerns. The obstacles to policing drugged driving are real, but the need to overcome them may be increasing according to a report issued by the Governors Highway Safety Association.