Same as the law of the highway in Germany, as it was explained way back when I learned it and followed it.
This is my true story, of a trip of about 100 miles to go to the airport at Frankfurt.
My car could cruise at 100 mph, and sometimes I needed to go into the passing lane to go around a slower driver.
So I’m in the passing lane, and a big BMW comes up behind me, flashing lights to ask me to move over, which I do when my pass is complete.
As the BMW flies by me, right on his tail is a Porsche flashing his lights asking the BMW to move over.
This all happened fast, and is burned into my memory as how the system works.
I figured the BMW wanted to go 110+ mph, and the Porsche faster still.
In those days a 911 Porsche would do about 130 mph tops.
I would see three left lanes of a four lane highway with each lane a car going faster than the one in the next lane to the right. Then when they had all passed all three cars moved into the far right lane.
A friend who drove in Germany told me if you are in the high speed lane on the autobahn doing 85 and you see a speck behind you about a mile away you better look to move over pretty soon.