Prosecutors and some lawmakers have long pushed for laws that would set a strict blood-level limit for THC, the key ingredient in cannabis. A driver over the limit would be deemed guilty of driving under the influence, just as with alcohol.
But such legislation has failed several times in recent years in the face of fierce opposition from marijuana advocates and defense lawyers, who claim a one-size-fits-all standard doesn't work for marijuana because it affects the body differently than alcohol.
On both sides, passions run high.
"I haven't had a car accident since I was 18, and I've had marijuana in my system for most of that time," said Paul Saurini, 39, one of many weed activists, or "wactivists," who spoke out against setting a firm blood-level limit during a public hearing in the state capital.
"We have to create some standards to protect public safety. Not doing so, in my opinion, is reckless public policy," said John Jackson, the police chief in Greenwood Village. "Any time you legalize things like this, you'll have more of it on the roadway."
The outcome of Colorado's struggle to shape marijuana-related DUI laws could have far-reaching implications, as a growing number of states approve marijuana for medical use and others consider legalizing the drug altogether.
Though research and opinions vary widely, studies have shown that smoking marijuana tends to affect spatial perceptions. Drivers might swerve or follow other cars too closely, as well as lose their concentration and suffer from slowed reaction times.
Such findings have led some researchers to conclude that driving high doubles the chances for an accident, and that smoking pot and drinking before driving is a particularly dangerous mix.
Every state bars driving under the influence. But convictions in drugged-driving cases generally rely on police officers' observations rather than blood tests.
Marijuana advocates argue that, unlike with alcohol, traces of the drug remain in the bloodstream long after an individual has smoked pot, and that a THC test can mistakenly suggest a person is high.
But officials who favor a blood-level limit say tests exist that can pinpoint "active" THC in the bloodstream in the hours immediately after marijuana usage.