The dominance of moral norms suggests that if a speed limit on a highway conflicts with a person's moral duty to rush a dying man to the hospital, then:

I believe the answer is: the moral duty would take precedence over the legal duty

dominance of moral norms conveys that when a moral norms are in a conflict with non-moral norms, the moral norms would be seen as the one that obtain the supremacy between the two. Usually, violating non-moral norms to fulfil a moral norms would make the punishment for the violation become void.

for your question the answer would have to be france