Does the but for test apply in cases involving negligent drivers?

27 One situation requiring an exception to the “but for” test is the situation where it is impossible to say which of two tortious sources caused the injury, as where two shots are carelessly fired at the victim, but it is impossible to say which shot injured him: Cook v. Lewis, 1951 CanLII 26 (SCC), [1951] S.C.R. 830. Provided that it is established that each of the defendants carelessly or negligently created an unreasonable risk of that type of injury that the plaintiff in fact suffered (i.e. carelessly or negligently fired a shot that could have caused the injury), a material contribution test may be appropriately applied.