The legal issue comes after the moral one. The questions posed is a classic choice of "sacrificing one to save more than one" an ethical dilemma, not a legal one. Laws may be written to codify the ethical decision that has been made but, the ethics must be resolved before laws can be created to uphold those morals.
Thanks for giving me the opening for this thought (Charliemopps)... While reading the article, I was again amazed by the lengths that some individuals will go to in order to avoid answering the moral question before them. In the case presented someone is going to die; either the driver or the two bystanders. It doesn't matter why the situation exists, it exists, we've gone past why. You must choose who will die as the dilemma dictates someone must die.
Stopping the car isn't an option that is available or putting it another way, stopping the car results in either the death of the driver or the two bystanders.