At the same time, traffic fatalities in which drivers had enough marijuana in their bloodstream to be deemed legally impaired dropped sharply, from 52 in 2016 to 35 last year.
The reason for this seeming contradiction: Marijuana can remain in the bloodstream for weeks, so a positive blood test may not mean a driver was stoned at the time of a deadly crash.
As the Colorado Department of Transportation study notes, “The presence of a cannabinoid does not necessarily indicate recent use of marijuana or impairment.”
Overall, the number of fatalities involving positive tests for marijuana has nearly doubled since recreational legalization in 2014, from 75 that year to 125 in 2016 and 139 last year.
Colorado law specifies that drivers with 5 nanograms of active tetrahydrocannabinol (THC) in a milliliter of their blood can be prosecuted for driving under the influence of marijuana.
A striking finding in the new study was the death toll involving people driving around with a cocktail of drugs in their bodies. In one year, deaths where drivers tested positive for cannabis, any alcohol and other drugs tripled – from eight in 2016 to 25 last year.
The report also found that drunken driving deaths had increased again. Twenty-six percent of those killed in crashes, or 171 people, had blood alcohol content of 0.08 percent or greater, Colorado’s drunken driving limit, compared to 161 in 2016 and 151 in 2015.
Meanwhile, traffic deaths generally continued to increase on state roads, going from 546 in 2015 to 608 in 2016 and spiking to 648 last year.
CDOT spokesman Sam Cole said the department considers the number of deaths in which the driver was marijuana-impaired under state law to be the most reliable indicator of its impact.
By that measure, marijuana-related deaths are clearly down.
“Presence does not indicate impairment,” he said. At the same time, “two years does not make a trend.”
Kristi Kelly, executive director of the Marijuana Industry Group, welcomed the state finding that marijuana-impaired highway deaths declined last year.
She added that the industry intends to keep campaigning against smoking and driving.
“We don’t think our job is done,” she said.
Henny Lasley heads Smart Colorado, a group concerned about the effects of legalization on children.
She worries that the latest highway death statistics will be used to loosen state regulations and promote public consumption of marijuana products.
First, “The science of impairment is lacking,” she said. “More concerning is why people are combining” marijuana, alcohol and other drugs, she said. “The combination is very concerning.”
Before fatal drug-related crashes, “drivers do tend to combine,” he said. “When you combine, it will amplify your impairment.”