Montana Title 61. Motor Vehicles § 61-8-311. Minimum speed regulations

(1) A person may not drive a motor vehicle at a speed slow enough to impede or block the normal and reasonable movement of traffic except when reduced speed is necessary for safe operation or in compliance with law.

(2) On a two-lane highway where passing is unsafe because of oncoming traffic or other conditions, the operator of a slow-moving vehicle behind which four or more vehicles are formed in line shall turn off the roadway at the nearest area where a sufficient and safe turnout exists in order to permit the vehicles following it to proceed. If the shoulder of the highway to the right of the slow-moving vehicle is wide enough and is in a condition allowing safe travel, the operator of the slow-moving vehicle may drive onto the shoulder and proceed at a safe speed until passed. As used in this section, a slow-moving vehicle is one that is proceeding at a rate of speed less than the normal flow of traffic at the particular time and place. The department of transportation is authorized to designate and construct turnouts and to erect official traffic control devices at appropriate places advising motorists of this statute.

(3) If the department of transportation or local authorities within their respective jurisdictions determine on the basis of an engineering and traffic investigation that slow speeds on any part of a highway impede the normal and reasonable movement of traffic, the commission or the local authority may set a minimum speed limit below which a person may not operate a vehicle except when necessary for safe operation or in compliance with law.