(CNN) -- Recreational weed may be legal in Colorado, but that doesn't mean people can smoke pot and get behind the wheel.
Josh Lewis, public information officer for the Colorado State Patrol, is warning drivers in his state that police will be vigilant about making sure the roads are as safe as they were before recreational weed became legal January 1 for those 21 and older.
"We have been dealing with marijuana and other narcotics throughout the history of narcotics and marijuana. It's really nothing new for us," Lewis told HLN. "We are going to do our jobs and enforce the law and make sure everyone is safe on the roadways. Ultimately, if the numbers show there are more people driving under the influence of marijuana so be it, but we are going to go out there and do our jobs day in day out."
Lewis said a state trooper's job of determining whether someone is intoxicated behind the wheel hasn't changed, and there are some tell-tale signs that will indicate whether an individual may have been smoking pot.
"Are their eyes bloodshot? Watery? Do they have trouble responding in a normal amount of time? Is there an odor of marijuana or something else going on?" Lewis said.
According to WebMD, a recent Yale University study found that both marijuana and alcohol impair driving-related skills, but the impairment effects of weed versus alcohol vary, depending on the person.
If police have a reasonable suspicion that a driver is high on weed, an officer will likely ask the driver to take a roadside sobriety test, which is the same test given to people suspected to be under the influence of alcohol or other drugs. If the driver fails or refuses to take the sobriety test, then the officer will have to decide whether to arrest the driver and conduct a voluntary blood test.
Lewis said samples used for the blood tests will be taken by medical professionals. He added that an ambulance could be called to the scene to take the sample, or a driver could be taken to a nearby emergency room to have the blood drawn.
Drivers can decline to take the blood test, but Lewis warns that refusing it could lead to harsher penalties in some respects.
"A person who refuses to cooperate with the expressed consent blood test will automatically have their license revoked for a year. Obviously, every situation is different -- it comes down to DAs and judges, but ultimately that person's license will be revoked on the spot for a year no questions asked versus if they were compliant and came back positive for marijuana or something they can actually get it back within a few months -- much sooner than if they had refused," said Lewis.
The results of the blood test could take two to six weeks to come back, according to Lewis. The legal limit of THC -- an active ingredient in marijuana -- that Colorado drivers can have in their blood is 5 nanograms per milliliter. That's a limit that Allen St. Pierre, the executive director of the National Organization for the Reform of Marijuana Laws, calls arbitrary and inaccurate.
"Measuring five nanograms does not measure impairment," St. Pierre said. "You can have individuals who have stopped using marijuana two weeks ago, two months ago. In some cases, if they were losing weight, they could still test over 5 nanograms."
Lewis said he has heard the criticisms of the marijuana DUI law that passed last year, but officers will only use a blood test after they have observed the driver being intoxicated.
"If we determine if someone is under the influence on the side of the road in that moment based on the observations, that is when we send off a blood sample," he said.
Ultimately, if someone is convicted of driving under the influence of marijuana, they could face some stiff penalties.
"The average DUI regardless of drugs or alcohol can cost between $10,000 and $11,000 once all the fines and court costs are added up as well as loss of license for a period of time," said Lewis.
In 2012, Colorado voters approved the sale of recreational marijuana, as did voters in Washington state. But Colorado is the first to have the pot shops up and running under regulations recently established by state and local governments. Washington retailers won't start selling recreational weed until later in 2014.
St. Pierre said voters in Oregon, Alaska and California could vote on similar initiatives in the next few years.
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