Ah. In my state, California, the passing lane rule only applies if you're not already going the speed limit or if there is traffic congestion, the normal speed

Ah. In my state, California, the passing lane rule only applies if you're not already going the speed limit or if there is traffic congestion, the normal speed of traffic. If you're going the speed limit, you are under no obligation to get out of the left lane just because someone behind you wants to speed. Regardless though you're supposed to move right if you're moving slower than the lane to your right. It appears that Illinois law also has an exception for traffic congestion, but not for speed limits.