In what circumstances will a plaintiff have to disprove negligence in a motor vehicle accident claim?

In Lalani v. Wilson, [1988] B.C.J. No. 2408, Lysyk J. observed that: …meaning must be attributed to the recognition in those judgments that the carrier is not an insurer. …in circumstances such as those here present, where the possibility of injury was not self-evident and no attention was drawn to such possibility at the time, the difficulties involved in imposing a legal obligation upon the carrier to disprove negligence are obvious. While expressed in positive terms of proving due care, in effect the carrier is being called upon after the event to prove a negative, that is, that the driver was not driving at an excessive rate of speed or had not failed to keep a proper look out or was not otherwise careless. I consider those observations apt in the circumstances here.