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How police officers determine marijuana impairment while driving


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Marijuana was legalized in Colorado in 2012. Now, it is legal for people to be under the influence of alcohol, marijuana or both. However, performing certain activities while under the influence of drugs or alcohol will remain illegal. If people are found to be under the influence while driving, they could be charged with a DUI or DUID.

People are often charged with a DUI or DUID after being stopped by a police officer for a traffic violation not necessarily indicative of impairment (such as speeding). People who speed are not always under the inebriated, but it does provide a police officer a basis to stop the person. Then, once they begin speaking with the driver it may become apparent that they are under the influence of alcohol, marijuana or another drug.

Next steps during a traffic stop

Officers generally at this time perform field sobriety tests such as having the driver perform a walk and turn test or stand on one leg and ask them to follow their finger with their eyes. Then, at least for alcohol, police officers can use a preliminary breath test while they are still on the road to determine whether the driver’s BAC is above the legal limit. However, there is not a similar test for marijuana.

Instead when officers are determining whether the driver is under the influence of marijuana, they must only rely on the physical tests. There are many police officers who are trained as Drug Recognition Experts (DRE) who administer many of the same tests as those used for alcohol detection, but DREs are specifically trained to detect the signs of marijuana intoxication.

What police officers look for in field sobriety tests

Officers are trained to look for a lack of convergence when drivers are following the officer’s finger with their eyes, pupil dilation, elevated pulse together with general signs of impairment from the other field sobriety tests to determine impairment. However, this evidence cannot be used in court to prove that drivers are under the influence of marijuana. After a driver is arrested, they will need to submit to a blood test to determine whether they have elevated levels of THC in their blood. The blood test is the evidence that would be used in court.

It is not as easy to determine if people are under the influence of marijuana as it is determining BAC levels for alcohol impairment. Even blood tests can present issues. It is difficult to determine how much THC is in the blood and why it is present. So, there may be defenses available to people who are charged with driving under the influence of marijuana that may not be present for people charged with driving under the influence of alcohol. Experienced attorneys understand these defenses and may be able to help protect one’s rights.

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