As a Human Factors Expert, Dr. Bong Walsh has been involved in many cases where a motor vehicle accident was blamed on a driver because the driver had alcohol, marijuana, or another substance in his/her system. Much of the time, the blame or “cause” is seemingly automatic or by default due to the presence of the substance. Using examples from actual cases that he has been involved with, Dr. Walsh will present practical information on defending drivers in situations where a result is blamed on driver impairment despite a lack of substantive evidence of a causal relationship between the presence of the substance and the driver’s actions or eventual result. Dr. Walsh will also present information specific to the interpretation of THC metabolite levels, using results and figures from peer-reviewed scientific journal articles.