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.
The GHSA report indicates that a growing percentage of drivers are testing positive for marijuana or other potentially impairing substances. Data collected by the National Highway Traffic Safety Administration shows that fatal car accident victims test positive for impairing drugs at approximately the same rate as they do for alcohol. In 2013 and 2014, more than 15 percent of drivers tested positive for marijuana or other illegal drugs. That figure does not include drivers who may have been impaired by legal drugs, such as prescription painkillers or anti-depression medications.
There is substantial debate about how certain substances impact a person's ability to drive safely. In general, it is clear that drugs like marijuana have some impact on crash rates. But people can test positive for marijuana long after it has stopped impairing their ability to drive. The law needs to protect people from impaired drivers, without making criminals out of drivers who were not driving unsafely. With marijuana use on the rise, it is important to find a way to protect the driving public in an intelligent and beneficial way.
Source: CNN, "Driving while drugged now just as deadly as drunk driving," by Carina Storrs, 1 October 2015