What is the standard of care required by the courts to determine negligence?

In Ryan v. Victoria (City), 1999 CanLII 706 (SCC), [1999] 1 S.C.R. 201, it is said: 28 Conduct is negligent if it creates an objectively unreasonable risk of harm. To avoid liability, a person must exercise the standard of care that would be expected of an ordinary, reasonable and prudent person in the same circumstances. The measure of what is reasonable depends on the facts of each case, including the likelihood of a known or foreseeable harm, the gravity of that harm, and the burden or cost which would be incurred to prevent the injury. In addition, one may look to external indicators of reasonable conduct, such as custom, industry practice, and statutory or regulatory standards. 29 Legislative standards are relevant to the common law standard of care, but the two are not necessarily co-extensive. The fact that a statute prescribes or prohibits certain activities may constitute evidence of reasonable conduct in a given situation, but it does not extinguish the underlying obligation of reasonableness. Thus, a statutory breach does not automatically give rise to civil liability; it is merely some evidence of negligence. By the same token, mere compliance with a statute does not, in and of itself, preclude a finding of civil liability. Statutory standards can, however, be highly relevant to the assessment of reasonable conduct in a particular case, and in fact may render reasonable an act or omission which would otherwise appear to be negligent. . . .