The U.S. National Highway Traffic Safety Administration has released a fact sheet that summarizes the likelihood of crash risks of drivers who are under the influence versus those who are sober, and those who drive after using marijuana versus those who have not used the drug.

While the extent of use of alcohol by drivers and the risks  posed by alcohol use have been well known for many decades, relatively little has been known about the use of  other drugs by drivers and the associated risks. However, drug-impaired driving has recently become an issue of increasing public and governmental concern in the United States and in many other countries (Compton et al., 2009; Asbridge et al., 2012; ICADTS, 2007).

While it is readily apparent that driving-related skills can be impaired by a wide variety of illegal substances and medications, the nature and scope of the drug-impaired driving problem has been difficult to define (Jones et al., 2003; DuPont et al., 2012; Houwing, 2013). In the United States, recent State actions to legalize the use of marijuana for medical and recreational use have further exacerbated concern over potential risks of driving impaired by marijuana.