Charged with cannabis impaired driving after passing the breathalyzer test

Police often switch their focus to cannabis after a driver passes the breathalyzer.

If the police, wrongly or rightly, believe someone is impaired they will make a roadside demand for a breath sample into an approved screening device (ASD). This test will show either pass, warn or fail. Police are supposed to have probable cause to make the demand meaning observations of signs of impairment. When a person passes an ASD breath test by blowing a 0 or something under the .05% BAC warning range, the officer will often then suspect the driver is impaired by drugs such as cannabis or a combination of cannabis and alcohol (crossfaded).

Some believe that since the officer’s initial belief was proven to be wrong (that the person was not drunk) they will automatically begin to believe cannabis must be to blame. As such, the phenomenon known as “tunnel vision” may occur leading the officer to wrongly look for confirmations of their now biased opinion that the person is not sober. The problem is that roadside observations and even more thorough tests by the “drug recognition expert” at the station are ultimately just a matter of opinion. They are not conclusive.

In Ontario, blood level THC testing is not always available as only a limited number of people are qualified to take the samples needed to conduct these tests. It is much harder for the police and Crown to prove in court that the accused was driving while high than it is with alcohol impairment.

Police can be wrong in their opinion that someone is driving while high particularly in cases where they wrongly suspected alcohol impairment first.

What happens to the accused is that “one thing leads to another” as the focus switches from alcohol to cannabis after they pass the breath test. The officer may feel compelled to be right and justify their observations. The DRE officer may also misinterpret the behaviour of the accused who is a person they do not know and are unfamiliar with.

Just because the police at the roadside and later at the station are of the opinion that you were high on cannabis (or something else) does not make it true. The opinion of the officers is just that - an opinion. Their opinion does not make you guilty. It makes you accused. Ultimately it is the judge in the court whose opinion will determine guilt or innocence. Judges acquit people of cannabis impaired driving in Ontario when reasonable doubt is raised.

In cases where the officer first suspects alcohol and then switches the focus of their investigation to cannabis impairment this may raise doubts as to the reliability of their evidence in court. The police may have been wrongly influenced by confirmation bias due to their initial belief of impairment. Ultimately, this is an important factor to be raised by your lawyer for the judge’s consideration.


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