A bill to make it easier to convict people of driving while stoned passed its first test in the Colorado legislature Monday.

Senate Bill 117 won approval in the Senate State, Veteran and Military Affairs Committee on a 4-1 vote after a nearly seven-hour hearing. It creates a limit on the amount of marijuana drivers can have in their blood before they're presumed too high to drive.

The bill also creates a zero-tolerance standard for the presence of numerous other drugs.

"The privilege of smoking marijuana should stop at the vehicle door," said the bill's sponsor, state Sen. Steve King, R-Grand Junction. He cited several fatal traffic crashes caused by someone driving high on marijuana or other drugs.

"How many dead is the number that will cause us to act?" he asked.

Critics of the bill said it goes too far and that safeguards against drugged driving are already in place.

"This is a radical bill," said attorney Rob Corry, who specializes in medical-marijuana law.

King's bill revives a proposal that gained traction in the legislature last year before it was ultimately rejected.

The current bill creates a "per se" limit for THC, the psychoactive chemical in marijuana. The limit would make it a crime to drive with more than 5 nanograms of THC per milliliter of blood in your system. King and others said numerous studies have shown that amount to cause impairment.

"We are at where we need to be with the science," said Cynthia Burbach, a state forensic toxicologist. "Five nanograms is more than fair."

Opponents of the bill, though, said other research shows not everyone would be impaired at 5 nanograms, leading to concerns that sober drivers could be convicted of driving under the influence of drugs per se.

"You are guaranteeing the conviction of innocent people," said medical-marijuana attorney Sean McAllister.

King's bill goes farther than last year's proposal by also making it a crime to drive with any amount of a Schedule I controlled substance, such as heroin or LSD, in your system. And the bill would create a "permissible inference" that drivers are impaired if they test positive for any amount of a Schedule II controlled substance — which includes drugs such as cocaine, oxycodone and codeine. A permissible inference is an instruction that "gives the jury a nudge," said Thomas Raynes, the head of the Colorado District Attorneys Council

Sen. Tim Neville, R-Littleton, opposed the bill over concerns that the Schedule II piece would stack the deck against innocent drivers. But Chris Halsor, also with the District Attorneys Council, said police officers would have to take several steps before ordering a blood test, meaning there would already be evidence of impairment.

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