Even in the leftmost lanes drivers are required to stay under the speed limit. In practice that is risky for slow drivers, especially in those states where drivers are armed.
True, but: few cops will arrest for 4-5 MPH over speed limit unless school zone. I see folks doing 50-70 mph in front of my house. It is 35 mph. These local cops have 2 main speed traps. I have asked them to stop this. They refuse.