What is the test for determining whether a defendant is liable in negligence in a motor vehicle accident?

A defendant is not liable in negligence unless their breach of the standard of care caused the plaintiff’s loss. The causation analysis involves two inquiries. First, the defendant’s breach must be a factual cause of the plaintiff’s loss. Factual causation is generally determined in accordance with the “but for” test; that is, the plaintiff must prove on a balance of probabilities that the harm would not have occurred but for the defendant’s negligent act: Marchi at para. 96; Clements v. Clements, 2012 SCC 32 at paras. 8 and 13. Second, the defendant’s breach must be a legal cause of the plaintiff’s loss, in that the plaintiff’s loss is not too remote. The remoteness inquiry asks whether the specific injury suffered by the plaintiff was a reasonably foreseeable consequence of the defendant’s breach: Marchi at paras. 97–99.