Better way to achieve slower traffic keep right

When I visited Italy, I was amazed at Italian drivers' courteous and considerate driving habit: before you pass a slower car, you're almost always guaranteed to have the left lane available for you to do so, even though before you come close to the point of passing, the slower car is in the left lane, or sometimes even running across both lanes. In the US, we have the Slower Traffic Keep Right sign everywhere on state or inter-state highways and yet far fewer drivers obey this rule than in Italy. One way to achieve the goal of slower traffic staying in the right lane is simple. Just make the pavement of the left lane rougher than the right lane. That way, driving in the left lane for an extended period of time is far noisier and less comfortable. In fact, when the road needs repairs, the government could even care less about the left lane, leaving small potholes alone for a longer time than those in the right lane. But that probably would not be a feasible strategy.