The NCSL Blog


By Mark Wolf

As states grapple with the increasing availability of legal marijuana, a set of panelists discussed approaches to curbing drug-impaired driving as they convened in downtown Denver, just a few blocks away from one of the nation's most convenient shopping districts for accessible and fully legal marijuana.

Jennifer Knudsen"We in Colorado are blazing a trail," said Colorado Representative Jonathan Singer (D), whose state was one of the first two states—along with Washington state—to legalize recreational marijuana. "A lot of the questions you're asking in your state, we are still asking."

The first presenter laid down a straightforward marker: "The growing body of evidence suggests that legalizing marijuana for recreational use is a gamble on the traffic safety side that states really ought not to make," said Richard Romer, manager of state relations for the American Automobile Association.

If states are going to legalize marijuana—and 1-in-5 Americans live in a state where recreational marijuana is legal and two-thirds of the country live in states where it is legal for medicinal purposes—Romer said the simplest thing for legislators to do is ensure they have enough data on drug-impaired driving to craft legislation.

And, he added, "'Per se' laws (those that set definitive standards for drug-impaired driving) are arbitrary and not based in science." Both Washington and Colorado have impairment standards of five nanograms of active tetrahydrocannabinol (THC)—the active psychoactive component of marijuana—per milliliter of whole blood.

Blood tests work for alcohol levels but not for marijuana, he said, because the level of THC in blood is different from the level in the brain, adding that it was unlikely a reliable blood test for THC would be developed. 

The next big thing in Colorado enforcement, said Singer, was use of impairment tests that are cognitive tests.

Jennifer Knudsen, Colorado's traffic safety resource prosecutor for the state District Attorney's Council, handed out copies of a 4-by-4-inch card, detailing indicators for Cannabis Impairment Quick Assessment designed for police officers to keep in their pocket. Example: "Eyes: Conjunctive Tissue (looks like pink eye in both eyes). Lack of convergence, Dilated Pupils." The card also details effects on psycho-physical tests, information processing and other indicators of impairment.

"Data collection is so difficult. When we get to court, how do we prove what was acutally the psychoactive that impaired," she said. Knudsen said she tells law enforcement officials they need to become drug recognition experts and know the cues for impairment. Prosecutors, she said, regularly have to fight in court about whether the standard battery of tests is applicable to marijuana.

Responding to an audience question about the revenue boost to state treasuries from marijuana taxes (28 percent in Colorado), Singer said states shouldn't sell marijuana reveue as a way to solve funding problems. In Colorado, the first $40 million in tax revenue goes to school construction. That, said Singer, is about what it costs to build one high school.

For more information, read NCSL's resources on drugged driving.

Mark Wolf is the editor of the NCSL Blog. 

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About the NCSL Blog

This blog offers updates on the National Conference of State Legislatures' research and training, the latest on federalism and the state legislative institution, and posts about state legislators and legislative staff. The blog is edited by NCSL staff and written primarily by NCSL's experts on public policy and the state legislative institution.