Impaired Driving Cases: Rats Don’t Drive

In one of her criminal impaired driving cases, the defence lawyer was going through her curriculum vitae on the stand and was lauding his defence alcohol expert instead. The defence went on and on about how his expert had published over a hundred studies on the effect of alcohol on rats and other laboratory animals.

“Why“, he demanded, “did you not publish any similar studies?”
Rita looked at the lawyer firmly and said politely,
“Because sir, rats don’t drive.“

Effective and succinct and it stopped any further line of questioning. As a junior forensic scientist at the time I probably would have responded a bit pompously something like:

“The pharmacokinetics and pharmacodynamics of alcohol in the rat are substantially different from humans and so would have little relevance in criminal court.”

Which would have gone way above the heads of the jury and the judge and would have invited further questioning and clarification. Sometimes a little humour is the best way of answering a question in court.

Rita’s response illustrated a fundamental principle that applies equally to criminal impaired driving prosecutions and civil cases involving personal injury or overserving liability: forensic evidence must reflect human biology and behaviour, not laboratory animal models.

The differences between rat and human alcohol metabolism extend far beyond simple scaling. Rats metabolise alcohol at rates substantially different from humans, exhibit different patterns of absorption and elimination, and demonstrate impairment responses that don’t translate reliably to human driving performance. When expert witnesses rely on animal studies to draw conclusions about human impairment in impaired driving cases, they introduce scientific uncertainty that undermines the reliability of their testimony.

At Wigmore on Alcohol, this principle guides all forensic analysis and expert testimony. Whether evaluating blood alcohol concentrations in personal injury litigation, assessing impairment timing in overserving liability claims, or providing expert opinions in criminal impaired driving matters, we rely exclusively on peer-reviewed human studies and established methodologies validated in human populations.

Rita’s elegant response also demonstrated another crucial skill for expert witnesses: the ability to communicate complex scientific concepts clearly and memorably. In impaired driving cases, juries and judges need to understand technical evidence about alcohol absorption, elimination rates, blood alcohol calculations, and impairment assessment. When experts lose their audience in technical jargon, even scientifically sound testimony loses its persuasive power.

Effective expert testimony requires:

• Clear, accessible language that avoids unnecessary jargon
• Direct responses that address the specific question asked
• Appropriate use of analogies or examples that resonate with lay audiences
• Confidence in defending methodological choices without defensiveness
• Understanding when brevity serves better than elaborate explanation

Over 700+ cases of testimony experience across Canadian courts has reinforced these lessons. Whether facing cross-examination in criminal impaired driving trials or presenting findings in civil personal injury cases, the most effective experts combine rigorous scientific methodology with clear, compelling communication.

In addition, she inspired me to include only human studies in my books on forensic toxicology and to rely on only human studies in court. This commitment ensures that every opinion offered in impaired driving cases, every calculation of blood alcohol concentration, and every assessment of impairment timing reflects the best available evidence from human research.

The relevance of this principle extends beyond criminal prosecutions. In personal injury cases where alcohol-related impairment plays a role, courts need expert testimony based on how alcohol actually affects human judgment, reaction time, coordination, and decision-making. Animal studies, regardless of their scientific merit in other contexts, simply cannot provide this foundation.

Wigmore on Alcohol provides forensic toxicology expertise for both criminal and civil matters involving alcohol impairment. Our services include:

• Blood alcohol concentration analysis and calculations
• Impairment timing assessments for accident reconstruction
• Evaluation of absorption and elimination patterns
• Expert testimony in personal injury and overserving liability cases
• Review and critique of opposing expert opinions
• Consultation on case strategy and evidence evaluation

Contact us for a free forensic evaluation now!

Every opinion we offer rests on human studies, court-accepted methodologies, and decades of experience in Canadian courts. We understand both the science of alcohol toxicology and the art of presenting that science persuasively to judges and juries.

Whether you’re prosecuting or defending an impaired driving case, pursuing or defending a personal injury claim involving intoxication, or addressing overserving liability questions, the quality of your expert witness can determine your outcome. Rita Charlebois taught that lesson with grace, humour, and unwavering commitment to scientific validity—principles that continue to guide forensic toxicology practice today.