Montana legislators are considering a bill that would revise the state’s DUI laws so that they establish a legal limit of 5 nanograms per milliliter (ng/ml) for the psychoactive ingredient in marijuana, delta-9-tetrahydrocannabinol (THC).

A blood test would determine a suspect's THC blood level, similar to how a breathalyzer test determines blood alcohol level. Proponents of the bill hope that, if passed, the legislation will aid efforts to prosecute drugged driving cases -- regardless of whether the drug was acquired through legal means.

The Montana House passed the bill by an 80-18 vote on Feb. 27, but the Senate has yet to vote on the legislation. On March 18, however, the Senate Judiciary Committee approved the bill on an 11-1 vote.

The bill’s sponsor, David “Doc” Moore (R-Missoula), indicated that the 5 ng/ml limit was chosen because it best approximates the impairment/sobriety level associated with the .08 blood alcohol content (BAC) limit already in DUI state law.

Twelve other states now have similar legislation on their books, Moore said during a Montana Senate Judiciary Committee hearing on March 15. Of those 12 states, Washington and Colorado are the most recent to pass such legislation.

“Washington has set this [5 ng/ml] level, and we know that Washington has legalized recreational use of marijuana,” Moore noted during the hearing. “My concern is that those people will be traveling through Montana. We want to send a clear message that we don’t want them driving impaired.”