What is the test for a driver’s impaired driving under the influence of alcohol?

Our B. C. Court of Appeal 1989 decision in Caissie v. I.C.B.C. held: “Negligence on his part might be of such a nature and degree that, in conjunction with independent evidence of impairment, it might provide proof on a balance of probabilities that incapacity to exercise proper control in fact existed. The question here is whether the evidence demonstrates, on a balance of probabilities that the negligent acts were of such a nature and degree as to be explainable only by compelling the inference that the influence of alcohol caused the negligent acts and that the effect of the alcohol was to render him incapable of proper control. This can be tested by asking whether the collision would have been avoided if the plaintiff had been sober.”