OK--I have used Farwell's Rules of the Nautical Road
and have actually written an article referencing the book. I have enclosed a link to the article at the end of this response.
In the maritime context:
1) A regulation describes the specific and exact required conduct a vessel should employ when a "Risk of Collision" exists;
2) In contrast, Rules prescribe the proper conduct, but not the specific action, a vessel should take in order to avoid a collision;
3) The difference reflects is: A Regulation requires obtaining the prescribed situational outcome to avoid a specific situation and a Rule provides the broad behavior on how to accomplish the regulatory requirement.
I wrote this article a couple of years ago:
CoastalBoating.net, Risk of collision for the recreational boater, Captain Andrew Seligman, Colregs, collisions at sea, international regulations,