Your last line is true, but generally speaking a person plus a bike will be heavier than a person alone. I rather like the marine Rules of the Road, because hierarchy is situationally dependent on the size and maneuverability of the vessel. A small sailboat under wind power, for example, usually has priority over a power-driven vessel, but that isn't true around large power-driven ships over a certain length due to the fact the large ship can't maneuver quickly.