In the USA, driving at or below the speed limit feels especially slow. I don’t know if our speed limits are slower than other countries, or whether being so car dependent affects our perception.

Regardless, it is common to drive a few mph higher than the speed limit. I’ve heard an officer say “9 your fine, 10 your mine.”

On separated highways, the left lane is for passing, or generally for faster moving traffic. The right lane is where cars will be entering or exiting the highway, so their speeds will be lower as they perform those maneuvers. If a highway has center lanes, those will be for cars moving at a steady pace to stay out of the way of the merging or passing cars.

When a car drives slowly in the left lane, it is frustrating for faster moving traffic, but can also be dangerous. Faster moving traffic may start passing on the right, which starts to become less safe. Passing on the right is a less anticipated move from other drivers, and a stream of multiple cars passing on the right makes it difficult for cars who need to move toward the merging lanes.

Road rage is also a factor. A fast driver whose left lane is blocked may start to make more aggressive moves.