What is the test for determining who is at fault in a motor vehicle accident claim?

The defendant relies on Mahe v. Boulianne, 2010 ABCA 32 [Mahe]. In Mahe, the plaintiff claimed against a farm owner for injuries sustained when he fell off a ladder that had been mounted on a platform constructed on top of the truck. The method of doing the work was suggested by the defendant, and the plaintiff proceeded with the recommended approach. The plaintiff fell off the ladder at a time when he was not protected with a safety harness or other precautions. On appeal, it was determined that the fault of the farmer was in failing to warn the plaintiff of a known defect. The fault of the tradesman was in failing to use the ladder in an acceptable way, in conjunction with appropriate safety equipment. It was ultimately determined that the plaintiff was 60% at fault and the defendant 40% for failing to warn of the known defect.