Legislation to set THC driving standards in Colorado has failed twice before. However, a new version that also tweaks alcohol DUI rules won unanimous approval during its first House committee hearing earlier this week.

Aiding this momentum are assorted news videos that purport to show the dangers of driving while stoned; see examples below. But the clips don't address many of the objections that helped kill the previous bills.

A CBS4 report on what the station refers to as "DWS" relies to a large degree on a package assembled earlier this month by KIRO-TV in Washington, where voters have also given permission to adults 21 and over to use and possess small amounts of marijuana. Washington also has a law that sets THC intoxication limits at five nanograms per milliliter of blood -- the same levels that will be established with the passage of the Colorado bill, HB 13-1114, which is on view below.

The KIRO report shows three volunteers who smoke, then climb into vehicles and attempt to navigate a driving course -- and mostly fail badly, by either going far too slow or swerving into cones set up to simulate roadways. Here's the main piece:

Unfortunately, there are problems aplenty with this demonstration. Blood tests subsequently showed that the drivers weren't at or near the five nanogram level after smoking, but way over it -- in one case more than three times as much, in another instance seven times. As such, the report adds no useful information about whether five nanograms is actually an effective measure of intoxication -- and it doesn't address the fact that readings above that total are common in frequent users like medical marijuana patients due to the way THC lingers in the system.

Example: Back in 2011, Westword medical marijuana critic William Breathes's blood had tested at nearly three times the legal amount while sober.

To address this issue, the authors of HB 13-1114 have added a new element to the latest measure: a "permissible inference" defense, that would allow people who test at five nanograms or above to present other evidence to prove that they weren't actually impaired. But marijuana attorney Rob Corry sees this change as only a slight improvement, making the new proposal 95 percent bad as opposed to 100 percent.

Here's an example of what's wrong with the measure from his perspective, as outlined in a letter to legislators that's also shared below.

Continue for more about driving while stoned, including videos and documents. Corry writes:

One case I tried to a jury in the past illustrates the point. In People v. Solimeo, Gunnison County Court Case No. 10T288, the driver had ten nanograms of THC in his blood. There was no accident or victim whatsoever in the case. Mr. Solimeo's performance on voluntary roadside tests was not perfect, but easily attributed to high winds frequent in Gunnison (even the sober State Patrol Trooper could not perform the roadside tests perfectly in the courtroom when asked to do so). Despite the ten nanograms, all evidence in the case showed that Mr. Solimeo was perfectly sober, driving well, and not a danger to anyone on the road that night. Mr. Solimeo was aware of the effects of THC on him and could easily compensate for them. Mr. Solimeo did not testify at trial because there was no real evidence against him, and any testimony from him would have been viewed as self-serving and defensive. Accordingly, the jury acquitted Mr. Solimeo of all charges, and even declined to find him guilty of the lesser included offense of Driving While Ability Impaired ("DWAI").

Likewise, Corry sees the "permissible inference" defense as "Guilty Until Proven Innocent" standard, since defendants would have to present evidence that they were actually sober despite blood test results, as opposed to the prosecution being required to establish their guilt.

Whether any of that will matter at this point is debatable. The THC bill received support from Democrats as well as Republicans this time around -- something that hasn't been the case in the past. And while the road may be a bit tougher in the Senate, everyone from members of the Amendment 64 task force to representatives of the marijuana industry have either endorsed the policy or are making no obvious efforts to stop it.

Here's the aforementioned CBS4 item, followed by outtakes from the main KIRO report. Also on view: the text of the bill and the complete Rob Corry letter.

Rob Corry Letter About Driving Under the Influence of Drugs Bill

More from our Marijuana archive: "THC driving bill, take three: Read draft language of proposed 2013 legislation."