This law requires that motorists (a) move over one lane, and (b) gradually decelerate as they are approaching any public safety or emergency vehicle in the breakdown lane where possible. The history of its inception can be found here.
As it is right now, the law is difficult to enforce because (a) hundreds of vehicles pass by public safety and emergency vehicles on a regular basis, and (b) it relies on the motorists’ ability to safety change lanes. Due to this, it’s common for police officers conducting a traffic stop to approach from the passenger side.
All fifty states have enacted this law. Since Hawaii was the final state to do it, there have been no attempts to repeal or modify how the law operates.