Expert pharmacological evidence about the possible effects of drug withdrawal on driving ability is admissible under s 137 of the Evidence Act 1995 (NSW) even where the expert cannot give a firm opinion of actual impairment, provided the evidence has probative value as circumstantial evidence relevant to the manner of driving and the risk of prejudice can be addressed by appropriate jury directions. The case confirms that such evidence is properly treated as circumstantial evidence going to explain the cause of a collision rather than as propensity evidence.
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