Yes the law says move over or slow down. As a former truck driver , it's safe to move over when you ( the person in the left lane ) can react and slow down. Not when it won't incovenience the driver behind to have to apply some brake. I pulled over as soon as possible to let those behind see and move over also. It was in my TRAINING to do just that . I can't tell you the number of 4 wheelers that when I pulled over ( only 5 or 10 miles slower than they were going and well in front zip to the right and fly by the cop on the side of the road! I also have cop relatives who tell story's, luckily they still can of close calls on road stops. The story goes both ways ! :-)