Expert Evidence and Over 80 Trials

Today's decision in R . v. Gibson 2008 SCC 16 is essential for counsel dealing with impaired driving cases. The case summary follows.

The accused, G and M, were charged with driving "over 80" after failing a breathalyzer test. The first breath sample taken from G provided a reading of 120 mg and the second a reading of 100 mg. The two breath samples taken from M each produced a reading of 146 mg. At their respective trials, G and M testified as to their pattern of drinking at the material time and adduced expert evidence to rebut the presumption in s. 258(1)(d.1) of the Criminal Code that the breathalyzer readings provided proof that their blood alcohol concentrations exceeded the legal limit at the time of driving.

The expert opinion evidence concerning the accused’s blood alcohol concentration at the time of driving was expressed in terms of a range of possible blood alcohol concentrations, given the amount of alcohol consumed, the pattern of drinking, and the accused’s age, height, weight and gender. In each case, the range of hypothetical blood alcohol concentrations "straddled" the legal limit of 80 mg. G’s expert testified that, if the pattern of consumption described by G was accurate, his blood alcohol concentration would have been between 40 and 105 mg at the time of driving. M’s expert provided a range of between 64 and 109 mg. In addition, the expert called on behalf of M tested his elimination rate more than six months after the alleged offence. On the basis of this test, the expert determined that M’s elimination rate was 18.5 mg per hour and that M’s blood alcohol concentration would have been 71 mg when he was stopped by the police.

The trial judge accepted both the evidence of G’s consumption and the expert evidence. He was left with a reasonable doubt that G’s blood alcohol content had exceeded the legal limit, and acquitted him. The Supreme Court upheld the acquittal. The Court of Appeal held that evidence of a hypothetical person’s elimination rates was not capable of rebutting the presumption in s. 258(1)(d.1), set aside the acquittal and ordered a new trial.

The trial judge convicted M on the basis that the expert evidence did not tend to show that his blood alcohol content had not exceeded 80 mg. Both the Court of Queen’s Bench and the Court of Appeal upheld the conviction.

Held (Binnie and Deschamps JJ. dissenting): The appeals should be dismissed. Per Bastarache, Abella, Charron and Rothstein JJ.: Straddle evidence constitutes an attempt to defeat the statutory presumption in s. 258(1)(d.1) and, as such, does not tend to show that the accused’s blood alcohol concentration did not exceed the legal limit at the time of the alleged offence. Straddle evidence merely confirms that the accused falls into the category of drivers targeted by Parliament — namely, those who drive having consumed enough alcohol to reach a blood alcohol concentration exceeding 80 mg. Parliament, in creating this offence, clearly regarded driving with this level of consumption as posing sufficient risk to warrant criminalization. It is therefore not enough to show, based on evidence about the accused’s pattern of consumption of alcohol during the relevant time period, that the accused consumed enough alcohol to exceed the legal limit, albeit in a quantity that would place him within a range that may be somewhat different from that which could be extrapolated from the breathalyzer reading. It is clear from the wording of s. 258(1)(d.1) that the presumption can only be rebutted by evidence that tends to show that the accused’s blood alcohol concentration did not exceed the legal limit and, hence, that the accused was not in the targeted category of drivers. In order to displace the presumption, the evidence must show, therefore, that based on the amount of alcohol consumed, the accused’s blood alcohol concentration would not have been above the legal limit at the time of driving, regardless of how fast or slowly the accused may have been metabolizing alcohol on the day in question. The court need not be convinced of that fact; it is sufficient if the evidence raises a reasonable doubt. Furthermore, because it is scientifically undisputed that absorption and elimination rates can vary from time to time, nothing is really gained by post-offence testing of an accused’s elimination rate. It is because of these inherent variations in absorption and elimination rates that the presumption of identity is needed in the first place. In order to facilitate proof of the offence, the presumption treats all persons as one person with a fixed rate of elimination and absorption. Short of reproducing the exact same conditions that existed at the time of the offence, assuming this is even possible, any expert opinion evidence based on actual tests would have to be given with the qualification that absorption and elimination rates vary from time to time, and therefore the accused’s blood alcohol level at the material time cannot be measured with precision. Ultimately, the best evidence an expert can provide is likely to be a range reflecting average elimination rates. The Court should not interpret this legislative scheme, which is intended to combat the social evils resulting from drinking and driving, as requiring accused persons, some of whom may well be battling with alcohol addiction, to submit to drinking tests in order to make out a defence. In the present appeals, the expert opinion evidence, in placing the accused’s blood alcohol concentration both above and below the legal limit at the time of driving depending on the accused’s actual rate of absorption and elimination on the day in question, did no more than confirm that the accused fell within the category of drivers targeted by Parliament and did not rebut the statutory presumption under s. 258(1)(d.1). Consequently, M’s conviction is upheld and, in G’s case, the order for a new trial is confirmed.

Per McLachlin C.J. and LeBel and Fish JJ.: Both expert evidence of alcohol elimination rates in the general population and straddle evidence can be relevant and are therefore not inherently inadmissible for the purpose of rebutting the presumption in s. 258(1)(d.1). However, the probative value of evidence based on rates in the general population will often be so low that it fails to raise a reasonable doubt that the accused had a blood alcohol content exceeding 80 mg. Not only do elimination rates vary between individuals, but each individual’s rate will vary depending on such factors as the amount of food consumed, the type of alcohol consumed and the pattern of consumption. Thus, evidence that the blood alcohol content of an average person of the sex, age, height and weight of the accused would have been at a certain level or within a certain range will rarely be sufficiently probative to raise a reasonable doubt about the presumed fact that the actual blood alcohol content of the accused at the time of the offence exceeded the legal limit. Expert evidence of the elimination rate of the accused as established by a test is potentially more probative of the blood alcohol content he or she had while driving than evidence based on elimination rates in the general population. However, because an individual’s elimination rate varies over time based on a number of factors, the probative value of evidence based on the elimination rate of the accused will logically depend on the number of variables controlled for in the elimination rate test. Evidence of the elimination rate of the accused at the time of the offence would be more likely to rebut the presumption in s. 258(1)(d.1) than mere evidence of the elimination rate of the accused under testing conditions. Straddle evidence will rarely suffice on its own to raise a reasonable doubt as to the accuracy of a breathalyzer result. Once straddle evidence is admitted, it will be left to the trier of fact to determine whether that evidence, considered in light of the evidence as a whole, raises a reasonable doubt as to the accuracy of the breathalyzer result. Straddle evidence and the other evidence relied on by the defence will warrant an acquittal only if it tends to prove that the blood alcohol level of the accused at the relevant time did not exceed 80 mg. A wide straddle range cannot be considered evidence to the contrary of the breathalyzer result, since it does not tend to prove that the accused was at or under the legal limit. Similarly, a range that is overwhelmingly above the legal limit may be of limited probative value. The more that is known about probabilities within the range, the more probative the evidence may be. To foreclose the possibility of straddle evidence raising a reasonable doubt and rebutting the presumption in s. 258(1)(d.1) would inappropriately restrict the ability of an accused to defend him- or herself. The wording of the provision gives no indication of a legislative intent to render the fictional presumption absolute or irrebutable in practice. It also leaves open the possibility of discrepancies between test results obtained at the time of testing and the blood alcohol content of the accused at the time of the offence. A mandatory presumption that requires the accused to raise a reasonable doubt about a fact that has not been proved by the Crown may prima facie be a limit on the presumption of innocence protected by s. 11(d) of the Canadian Charter of Rights and Freedoms that needs to be justified under s. 1. In these cases, the expert’s straddle evidence adduced by G is sufficiently relevant to be admissible and is not without foundation. However, given that it is based on elimination rates in the general population, consists of a wide range of values and includes values significantly above the legal limit, it does not, as is required to rebut the presumption in s. 258(1)(d.1), raise a reasonable doubt that G’s blood alcohol content actually exceeded 80 mg. Although the expert evidence adduced by M was also admissible, it would have been unreasonable for the trial judge to find that the straddle evidence indicating a range of 64 to 109 mg was capable of raising a reasonable doubt. The evidence of M’s own elimination rate, which supported a blood alcohol content of 71 mg, was also rejected by the trial judge because the test used to determine the elimination rate had not sufficiently approximated the conditions at the time of the alleged offence, which limited its relevance to the fact M was seeking to prove. There is no reason to interfere with that finding. In the result, M’s conviction is upheld and, in G’s case, the order for a new trial is confirmed.

Per Binnie and Deschamps JJ. (dissenting): Evidence that tends to show that the blood alcohol concentration of the accused at the time of interception did not exceed the legal limit based on an elimination rate of 15 mg per hour, or on the actual elimination rate of the accused according to test results, will suffice to raise a reasonable doubt. There is a body of scientific evidence that shows that members of the general population tend to eliminate alcohol at a rate faster than 15 mg per hour. It would therefore be speculative to assume, without any evidence, that a given accused is different from the majority of the general population and is a slow eliminator. Unless the scientific information that supports using 15 mg as a marker is contradicted by persuasive expert evidence, a judge should acquit if the prevailing direction of the straddle range favours a level that does not exceed the legal limit. The prevailing direction approach affords the accused a defence that is sufficiently complete without requiring post-offence testing. As a matter of judicial policy, requiring accused persons to submit to drinking tests should not be encouraged by the courts. Nevertheless, post-offence testing is not, per se, irrelevant or lacking in probative value. Just as evidence of average elimination rates in the general population is not discredited simply because such rates do not replicate the situation of an accused, evidence of post-offence testing designed to determine the elimination rate of an individual accused should not be rejected for that reason alone. An elimination rate based on test results may constitute evidence that tends to show that an accused eliminates alcohol at a rate faster than 15 mg per hour. Although the weight given to post-offence testing may depend on a number of variables, this should not be interpreted as requiring replication of the conditions of absorption. In G’s case, the expert for the defence testified that G’s blood alcohol content while he was driving would, based on average elimination rates, have been between 40 and 105 mg. There is agreement with the trial judge’s finding that the prevailing direction of the range favoured a level that did not exceed the legal limit, and that this was sufficient evidence for an acquittal. Therefore, G’s acquittal should be restored. In the case of M, the Crown failed to undermine the weight of evidence of post-offence testing by either cross examining the expert or adducing contradictory expert evidence at trial. Although M’s elimination rate according to the expert’s test may not be the same as his rate on the day of the offence, nothing in the record suggests that any variation between the actual and tested elimination rates would be material or would cast doubt on the usefulness of the expert evidence. Nevertheless, the expert’s post-offence tests can constitute evidence to the contrary only if M’s consumption scenario is found to be credible. Here, the trial judge made no express findings on this issue. He rejected the expert’s evidence on the basis that the midpoint of the straddle range was above the legal limit and that the food and the type of alcohol consumed had not been taken into account in the post-offence tests. As he had dismissed the expert testimony, the trial judge found M guilty without making any findings concerning his credibility. Since this Court cannot enter an acquittal, as a finding on M’s credibility would have had to be made first, a new trial should be ordered on the charge of driving with a blood alcohol level exceeding the legal limit.