Purpose This study will present the prevalence of self-reported marijuana and alcohol impaired driving, compare perceived risks of driving under the influence of alcohol versus marijuana, and examine risk factors associated with impaired driving.

Methods Data are from a telephone survey conducted by the Colorado Department of Transportation in 2014. The survey included questions assessing substance use, perceptions of risks and consequences related to impaired driving, and frequency of impaired driving among a representative sample of Colorado adults. The sample (n = 770) was weighted to reflect the 2010 Census estimates for Colorado.

Results Few respondents perceived it safe to drive under the influence of alcohol (6%). However, those who reported past month marijuana use were more likely to report that they could safely drive after using marijuana (49%) compared to those that did not use in the past month or those that used alcohol in the past month. Of those that used marijuana in the past month, 73% endorsed marijuana impaired driving is safer than alcohol impaired driving. Marijuana users reported driving under the influence of marijuana on an average of 5.1 days in the past month compared to alcohol users who reported driving alcohol impaired on 1.2 days. Marijuana impaired drivers were more likely to be male, younger (18–34) and have some college education as compared to a bachelor degree or more education.

Conclusions Perceptions of risk associated with marijuana impaired driving is lower than that associated with alcohol, particularly for current marijuana users. Current marijuana users drive impaired more frequently than alcohol users.

Significance Understanding who drives impaired and their perceptions of risk can inform prevention messaging and public awareness campaigns.