Mich. Comp. Laws § 257.62: “Special mobile equipment” defined.

Sec. 62.

"Special mobile equipment" means every vehicle not designed or used primarily for the transportation of persons or property and incidentally operated or moved over the highways, including farm tractors, road construction or maintenance machinery, mobile office trailers, mobile tool shed trailers, mobile trailer units used for housing stationary construction equipment, ditch-digging apparatus, and well-boring and well-servicing apparatus. The foregoing enumeration shall be considered partial and shall not operate to exclude other vehicles which are within the general terms of this definition. Although not within the general terms of this definition, the combination of a mobile car crusher trailer permanently attached to a truck tractor or road tractor shall be considered special mobile equipment for purposes of this act.