In most ‘over 80’ cases, the Crown relies upon something called the ‘presumption back’ or the ‘presumption of identity’ to gain a conviction.
What typically happens in an ‘over 80’ case? The accused person is pulled over while driving, taken to the police station and breath tested some time well after the driving. What do those breath tests then reveal? What they reveal is the blood-alcohol concentration of the subject at the time the test was administered. Of course, what the Crown has to prove is the blood-alcohol concentration at the time of driving – not at the time of testing. It is, after all, not an offence to be over the legal limit while being tested, only while in the care or control of a motor vehicle.The breath tests taken at the police station tell us only the blood-alcohol concentration at the time of testing – not driving.
How then are they used to prove that the accused person was over the legal limit at the time of driving? One available method is for the Crown to call an expert witness to relate the blood-alcohol readings back to the time of driving. This, however, is not the most common method. The most common method is by utilizing the ‘presumption back’ or the ‘presumption of identity’. The ‘presumption back’ is an evidentiary short cut enumerated in the Criminal Code of Canada. It states that, provided certain pre-conditions are met, the Crown is entitled to rely on the presumption that the lowest reading obtained at the time of testing is equal to the reading at the time of driving.
In most cases where the Crown is unable to rely on the ‘presumption back’, it is unable to prove the case. This typically happens where it is not in a position to prove the pre-conditions that allow it to rely on the presumption back. As an example, a pre-condition that the Crown must prove is that the breath tests were taken as soon as practicable. If it is unable to do that, then it will not be able to rely on the presumption. Many ‘over 80’ charges are successfully defended on this point. It typically arises where there is an unaccounted for period of time between the arrest and the testing where the Crown has either neglected to or is not in a position to call evidence to explain what happened during a certain period of time before the testing.
Without this evidence, the Crown may not be in a position to demonstrate that the tests were taken as soon as practicable. Without being able to prove that, it will not be allowed to rely on the ‘presumption back’. Without the ‘presumption back’, it will not be able to prove the blood alcohol concentration at the time of driving and the charge will be dismissed. Of course, as I mentioned earlier, the Crown has the option of calling an expert witness to relate the breath test readings back to time of driving but such a way of proceeding tends to be the exception rather than the rule.