I have been driving divided highways for fifty years and all that time there have been signs saying "Slower traffic keep right." It amazes me that there are people who do not understand that simple instruction. But there are, and they apparently need more than a sign to induce considerate and safe behavior.
Highway driving is not a game as some juveniles here like to think. If voluntary orderliness won't work, then ticketing may. If you are one who likes to camp in the left lane, you brought this on your self.