"The increase in law enforcement officers who are trained in recognizing drug use, from 129 in 2012 to 214 in 2018, can increase drug detection rates apart from any changes in driver behavior.
"Traffic safety data were obtained from a number of different sources. Please note that traffic safety data may be incomplete because law enforcement officers may determine that alcohol is impairing the driver, and therefore additional (time consuming and costly) drug testing may not be pursued.
"The total number of DUI citations issued by the Colorado State Patrol (CSP) decreased from 5,705 in 2014 to 4,849 in 2017. The prevalence of marijuana or marijuana‐in‐combination identified by Patrol officers as the impairing substance increased from 12% of all DUIs in 2014 to 15% in 2017.
"In 2016, the most recent data available, 27,244 cases were filed in court that included a charge of driving under the influence; 17,824 of these were matched with either a breath or blood test.1
"Of these, 3,946 had blood samples screened for the presence of marijuana: 2,885 cases (73.2%) had a positive cannabinoid screen and a follow‐up confirmation for other cannabis metabolites, and 47.5% detected Delta‐9 THC at 5.0 ng/mL or above.
"According to CDOT, the number of fatalities in which a driver tested positive for Delta‐9 THC at or above the 5.0 ng/mL level declined from 52 (13% of all fatalities) in 2016 to 35 in 2017 (8% of all fatalities).
"The number of fatalities with cannabinoid‐only or cannabinoid‐in‐combination positive drivers increased 153%, from 55 in 2013 to 139 in 2017.
"However, note that the detection of any cannabinoid in blood is not an indicator of impairment but only indicates presence in the system. Detection of Delta‐9 THC, one of the primary psychoactive metabolites of marijuana, may be an indicator of impairment.
"A 2017 survey conducted by the Colorado Department of Public Health and Environment found that 3.0% of adults reported driving within two‐to‐three hours of using marijuana in the past‐30 days, while 19.7% of recent marijuana users reported this behavior."
Impacts of Marijuana Legalization in Colorado: A Report Pursuant to Senate Bill 13-283. Colorado Department of Public Safety, Division of Criminal Justice, Office of Research and Statistics. October 2018, pp. 2-3.