I wonder if that legally prevents 2 semi trucks going under the speed limit from having the slowest drag race ever as the one in the left lane seemingly goes 1 MPH faster than the guy in the right lane for a couple mile stretch of 2 lane highway until the left lane truck finally gets far enough ahead to safely move back into the right lane.In South Carolina, for example, the law behind the "slow traffic keep right" signs is actually "no leftmost lane unless passing (barring congestion etc...)". So, paralleling someone in the lane to your right is in fact often illegal even if you are going the speed limit.