A bill making it easier to convict people of driving high on marijuana was among the more than two dozen bills sacrificed in the Colorado House Tuesday night during a gridlocked debate over civil unions.

Senate Bill 117, which was only two vote-counts away from the governor’s desk, failed to receive a second-reading vote by midnight. Bills cannot receive second-reading and final-reading OKs on the same day, meaning the bill is dead for the year. Wednesday is the last day of the legislative session.

Earlier in the day, the controversial bill surmounted its final legislative committee, when the state House Appropriations Committee approved it 9-4.

The proposal would have made it illegal to drive with more than a certain amount of THC — the psychoactive chemical in marijuana — in your system. The limit of 5 nanograms of THC per milliliter of blood that the bill proposed would have been similar to the .08 blood-alcohol standard for drunk driving.

Supporters said the bill was scientifically sound and was needed to send a message that driving stoned is not OK. Opponents said the limit was too low and would have resulted in near-certain convictions of sober drivers.

It is already against the law to drive high, but currently prosecutors must prove impairment on a case-by-case basis. Setting a limit — known as a per se standard — provides a shortcut around that.

In a statement released late Tuesday, the head of the Medical Marijuana Industry Group, a lobbying organization that opposed the bill, said the current law is effective enough at stopping stoned driving.

“We will continue partnering with state agencies, such as the Colorado Department of Transportation, to build awareness about the dangers of drugged driving, and to help make our roads safer,” Mike Elliott, the group’s executive director, wrote in an e-mail.

Lawmakers in the state Senate killed a nearly identical bill in the closing days of last year’s session. The Colorado Commission on Criminal and Juvenile Justice didn’t endorse this year’s bill, after an offseason subcommittee created to study stoned driving couldn’t agree on a proposal.

But, with the backing of law enforcement and drug-treatment groups, the bill squeaked through the Senate. It appeared headed for approval in the House before Tuesday night’s pile-up.

John Ingold: 303-954-1068 or jingold@denverpost.com