Initiative 502, which legalized marijuana in Washington state, also established a new standard for driving under the influence of a drug (DUID): Any motorist with five or more nanograms of THC per milliliter of blood is now automatically considered too stoned to drive, even if he isn't. Colorado's marijuana legalization initiative, Amendment 64, did not address the DUID issue, but the state legislature is considering a variation on the five-nanogram standard that also could result in the conviction of motorists who do not actually pose a threat to public safety.
The Colorado General Assembly has rejected a five-nanogram cutoff twice before because of doubts about whether it is a good measure of impairment. Experiments, including tests by TV stations in Seattle and Denver, indicate that many people can drive competently at THC levels far above five nanograms, especially if they are regular consumers who have developed tolerance and become accustomed to marijuana's effects.
But in February, Colorado's House Judiciary Committee unanimously approved a bill that would allow DUID convictions based on nothing more than a five-nanogram reading. Unlike a per se standard, the bill—which was endorsed by the Amendment 64 Implementation Task Force, a panel appointed by Gov. John Hickenlooper to advise the legislature on how to regulate marijuana—would not make people automatically guilty of DUID at five nanograms; instead that would be a "permissible inference." Defendants could avoid conviction by presenting evidence that they were not in fact impaired.
Under current Colorado law, the burden is on the prosecution to show that a driver was under the influence. Blood test results are one kind of information prosecutors can use, along with evidence such as erratic driving and poor performance on roadside sobriety tests, but they are not conclusive. A "permissible inference" rule, by contrast, would in effect establish a rebuttable presumption of impairment at five nanograms.
"What it does is shift the burden of proof," says Rob Corry, a Denver attorney and marijuana activist. "A person coming into court is guilty until proven innocent.…If you put a number on it, juries are going to latch onto that five-nanogram number, whether it's a permissible inference or a per se [standard], and the effect will be that innocent people are convicted, whether or not they're impaired."