From the Michigan DNR:
A snowmobile may be operated on the right-of-way of a public highway (except a limited-access highway) if it is operated at the extreme right of the open portion of the right-of-way and with the flow of traffic on the highway. Snowmobiles operated on a road right-of-way must travel in single file and shall not be operated abreast except when overtaking or passing another snowmobile.
A snowmobile may be operated on the roadway or shoulder when necessary to cross a bridge or culvert if the snowmobile is brought to a complete stop before entering onto the roadway or shoulder and the operator yield the right-of-way to any approaching motor vehicle on the highway.
Snwmobiles may be operated on a highway in a county road system, which is not normally snowplowed for vehicular traffic; and on the right-of-way or shoulder when no right-of-way exists on a snowplowed highway in a county road system, outside the corporate limits of a city or village, which is designated and marked for snowmobile use by the county road commission having jurisdiction.
