Depends on the state. In Colorado passing on the right is legal (though I personally find it barbaric). However, Colorado has a "left lane law" that applies on

Depends on the state. In Colorado passing on the right is legal (though I personally find it barbaric). However, Colorado has a "left lane law" that applies on two+ lane highways with speed limits above 65mph. It is illegal to impede traffic in the passing lane, even if you're going the speed limit. https://codes.findlaw.com/co/title-42-vehicles-and-traffic/co-rev-st-sect-42-4-1013.html https://codes.findlaw.com/co/title-42-vehicles-and-traffic/c... A different law requires drivers in the passing lane driving below normal and reasonable speed, to change lanes (move to the right or pull off the road). If you're driving at the speed limit, it's by definition not less than normal or reasonable. And prior to the "left lane law" state patrol couldn't do anything about impeded left lane traffic so long as the impeding vehicle was moving at the speed limit, but since the 2004 "left lane law" you can be ticketed for impeding traffic in the passing lane even if you're driving at the speed limit (and you were always subject to ticketing if you were driving below the speed limit in the passing lane).