Here are some things I believe would help in my experience. The left lane should be for passing only, if you are not passing someone, you should not be in it. This not only slows traffic, but also causes accidents because people have to pass on the right, and of course, that's when the slower car speeds up to prevent the other car from passing on the right. The other issue is trucks in the left lane on hills. I get it, they have to pass slower trucks, but then they end up below the speed limit on these hills and also slow traffic.