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DENVER — Colorado voters will decide this November whether marijuana should be legalized.  If it passes then marijuana would be regulated the same way as alcohol.

Click here to read Amendment 64—the referendum to legalize marijuana.

But right now there is no standard to determine if you’re too stoned to drive while under the influence of pot.

State lawmakers have proposed limits to set a standard but many argue those tests wouldn’t be accurate enough to determine impairment.

On Tuesday the state legislature killed the most recent proposal to set a marijuana impairment standard for drivers out here on Colorado’s roads.

But there’s no doubt it will come up again next session. 

FOX31 Denver is answering your questions by putting that proposed state standard to the test.

So what happens when someone who has been smoking marijuana gets behind the wheel?

It’s not just for recreational use; in Colorado, more than 89,000 people are legally licensed to buy marijuana to treat medical problems.

Patients’ conditions include fibromyalgia, severe pain, insomnia, and psychomotor agitation.

Whether it’s being used legally or not the question remains the same.

Will someone using marijuana put themselves–or you–in danger out on the road?

We wanted to find out for ourselves. So we setup a test using a simulator, police officer, and a group of volunteers.

Ranging in age from their early 20s to their mid 60s, our volunteers let us test not only their driving skills but their THC levels both before and after taking their marijuana.

Just this past week Colorado lawmakers narrowly voted down a new law that would have made it illegal for a person to drive with a specific THC level known as “Delta 9 concentration.”

If passed, any Colorado driver would be considered impaired if they had more than 5 nanograms per milliliter of marijuana in their blood.

“It’s all a variable on the person, each person came out with different numbers,” says Sarah Knill, a phlebotomist who routinely checks for drugs in blood.

But before we even started our driving test, a surprise–we found at least two of our volunteers would be considered impaired, under the recently proposed state standard, even though they hadn’t smoked or ingested marijuana all day.

But for police – the blood test is far from the first sign a driver is impaired.

“The indicators of their impairment come out through their speech, how they speak, physical observations, and just comments that are made,” says Officer Mark Ashby, who is a Colorado drug recognition expert. Ashby helps cops across the state figure out what an impaired driver may look like.

That’s why we asked him to watch our drivers just as he would from a patrol car.

Would he pull them over or let them keep driving?

We used a commercial driving simulator to take the place of an SUV and instead of downtown Denver – it’s a Sim City.

After a few minutes of practice, most of our group gets the hang of it.

23-year-old Max was eager to try our test and, even though he had not smoked his medical marijuana all day, the blood test shows he’s already above 5ng/ml limit.

“When I medicate, I actually come back down to what you would consider a more normal state.”

But after lighting up for our test, was there a difference?

“The difference between his second time and his first, he was significantly worse,” Ashby says.

Max’s take?

“Overall, I feel like I was little more calm, more stable, then I drove that time,” he says.

Our blood test shows Max may have already been considered impaired before he lit up; his first blood test came back at 6 nanograms – one above the previously proposed limit.

But after smoking for us, that number increases five-fold to 32 nanograms.

“Somebody who smokes on a regular basis for a year is going to be able to handle more than someone who doesn`t,” says Knill. “That’s just how the body works”

“I’m scaring myself.” That’s what our next volunteer said while she was behind the wheel.

For experienced drivers, like 63-year-old Fran of Littleton, driving after taking her marijuana is a challenge. 

“At least it is make believe crashes,” she says.

“She showed a lot of mental impairment,” Ashby says. “Not really just a physical impairment; she was stopping for no reason in the roadway.”

Officer Ashby would have pulled Fran over.

But the results of Fran’s blood test are shocking.

“She would have passed that test for Delta 9 because nothing showed up in her system,” Knill says.

That’s right; Fran’s blood test comes back clean.

The results show there’s no Delta 9 in her system even though she ingested her pot an hour before the test.

She says she wouldn’t trust herself behind the wheel either on the simulator or the real world.

“I don’t care if they’re taking oxycodon or Advil or anything, if you’re feeling a buzz, you don’t want to be driving.”

61-year-old Robert says he won’t drive right after smoking – maybe now we know why.

“He’s driving about 15-20 mph under the speed limit, he’s stopping before the stop lines 10, 15 feet before he should,” says Ashby.

After the test, Robert says with the marijuana in his system, he shouldn’t be allowed in the driver seat.

“I’m not used to driving when I have a buzz on, and I don`t do that personally. I wouldn`t have driven knowing I could wait an hour,” Robert says.

Before smoking marijuana, Robert showed 1.9 nanograms of delta-9 in his system. But afterward that number jumps way up to 10 nanograms—that’s double the limit lawmakers were considering.

“I felt a little more nervous about it this time, but I don’t think I would have killed anybody,” says Robert.

None of our volunteers put much faith in the simulator but can you put faith in the Delta-9 law when two people who admit they’re under the influence would pass with flying colors?

“I think there should be another way to base it on, not a five monograms because it affects everyone so differently,” says Knill.

The goal of any law is to protect yourself or others.

None of our drivers under the influence aced the simulator, but that’s why Officer Mark Ashby says any impairment should keep you off the road.

“It doesn`t matter what the chemical is. If the impairment is from drugs or alcohol, you’re breaking the law,” Ashby says.

The 5 nanogram proposal died in the legislature Tuesday, but the issue is expected to come up again when the legislature reconvenes in January.

That’s because even if the referendum to legalize pot does not pass this November, there are still medical marijuana users on these roads. 

So the question remains: How do you measure when someone’s too impaired to drive under the influence of marijuana.