Montana Title 61. Motor Vehicles § 61-10-128. When authorities may restrict right to use roadway

(1) A local authority may not alter the limitations provided in 61-10-101 through 61-10-104 and 61-10-106 through 61-10-110 or substitute other limitations or requirements, except as provided in this section.

(2) The department of transportation by order, or a local road authority by ordinance or resolution, may prohibit the operation of or impose restrictions on the weight and speed of a vehicle traveling on a public highway under its respective jurisdiction and for which it is responsible for maintenance whenever the highway will be seriously damaged or destroyed by deterioration, rain, snow, or other climatic conditions, unless the use of vehicles on the highway is prohibited or the permissible vehicle weights and speed are reduced. The department of transportation or the authority that enacts the ordinance or resolution shall erect signs designating the department's order or the authority's ordinance or resolution at each end of that portion of the highway affected, and the order, ordinance, or resolution is not effective until the signs are erected. The department of transportation or the authority by ordinance or resolution may prohibit the operation of trucks or other commercial vehicles or impose limitations on their weight on designated highways, subject to the provisions of subsection (3). These prohibitions and limitations must be designated by appropriate signs placed on the highways.

(3) Neither the department of transportation nor a local authority may prohibit the operation of or impose a restriction on the weight of a vehicle loaded with perishable seed potatoes or a vehicle loaded with fertilizer that is traveling on a public highway if:

(4) Hay grinders and their towing units are exempt from weight limits imposed by the department of transportation under this section.