What is the test for negligence in a motor vehicle accident?

I think the law is well stated in part of the headnote to Ouellet v. Cloutier, 1947 CanLII 35 (SCC), [1947] S.C.R. 521, as follows: The fact that it was possible that an accident might occur is not the criterion which should be used to determine whether there has been negligence or not. The law does not require a prudent man to foresee everything possible that might happen. Caution must be exercised against a danger if such danger is sufficiently probable so that it would be included in the category of contingencies normally to be foreseen. To require more and contend that a prudent man must foresee any possibility, however vague it may be, would render impossible any practical activity. As I understand the law, there is no obligation on a driver to keep himself specially prepared for action in an unforeseen emergency and it is only where the possibility of danger emerging is reasonably apparent that special precautions must be taken.