What is the test for determining liability for a following driver who runs into another vehicle from the rear of the vehicle?

In addition, the trial judge’s approach was wrong in law, in my view. The common law principle enunciated in Beaumont v. Ruddy does not prescribe that a following driver is always at fault if he or she runs into another from behind. It simply states that generally speaking this will be the case, and shifts the onus to the following driver to show otherwise. There is no principle of law of which I am aware that automatically fixes a following driver who runs into another vehicle from the rear with liability “no matter what [the lead driver] chooses to do, within [his or] her own lane.” Subject to the law’s general bias in favour of fault on the part of the following driver and the “following too closely” jurisprudence, liability – as in any negligence case – depends upon whether the following driver was acting reasonably in the circumstances and, conversely, whether the lead driver was as well.