Driving in Left Lane Isn’t Illegal in South Dakota
The South Dakota Highway Patrol shared a video on Facebook that was eye opening to me. They also pointed out while dangerous, it isn't illegal to camp out in the left lane of a highway in South Dakota.
The law does say that "slow moving vehicles" must not use the left lane. But it doesn't require the left lane to only be used for passing.
So basically, the law is for tractors and combines going slow and not those who obliviously camp out in the left lane after not using their turn signal to get there and never thought to go back to the right lane even though they are going two miles per hour slower than every other vehicle on the Interstate.