Its a pretty common law I would think. In WI, it's the same thing, if an officer is on the shoulder with it's emergency lights on, drivers must change into the next lane(if it's a 4 lane hwy or more, not a 2 lane). If there is absolutely no way to change lanes, you have to slow down when passing that police cruiser. The law is put in place to protect the driver and occupants that are on the side of the road, including the officer.
Even though its a law, a surprising number of people just dont know about it or are too stubborn to follow it. Sometimes you dont find out of these laws until you break them.