On any highway with more than one passing lane in the same direction, heavy commercial vehicles, except buses, shall be restricted in ordinary operation to the right-hand travel lane, and in overtaking and passing shall be restricted to the next adjacent passing or travel lane, and shall not use any other lanes except in an emergency. For the purpose of this section, heavy commercial vehicles shall be defined as those in excess of two and one half tons used for transportation of goods, wares, and merchandise.
Massachusetts Legal Code