The Train Dilemma

Unlike dilemmas such as in game theory, where there is a type of decision, i.e. preference for a particular option, as in the prisoner’s dilemma, in a moral dilemma such as the train dilemma is there a decision at all? In other words, are there moral rules by which one can rule in this honorable dilemma? And can this be compared to the case of a siege of a city where they say, “Give one man or you all die,” where the law does not say “give the man away”?