Mont. Code Ann. § 61-8-309

(ii) In the event of a vehicle emergency, adverse weather condition, or identification of another highway safety factor that warrants decreasing the speed limit for reasonable and safe travel, the commission may, in advance of the safety event, adopt localized geographic area temporary special reduced speed limits that are lower than a speed limit set by 61-8-303 or 61-8-312. The temporary special reduced speed limit becomes effective upon posting appropriate fixed or variable signs and shall remain in effect while the fixed or variable signs remain posted.

(1) (a) (i) If the commission determines upon on the basis of an engineering and traffic investigation that a speed limit set by 61-8-303 is or 61-8-312 greater is greater or less than is reasonable or safe under the conditions found to exist at an intersection, curve, or dangerous location or on a segment of a highway less than 50 miles in length under its jurisdiction, the commission may set or on a reasonable and safe special speed limit at that location. highway corridor under its jurisdiction greater than 50 miles in length on which increased crash frequency or fatal crash data is observed, the commission may set a reasonable and safe special speed limit at that location or corridor. In the case of a school zone adjacent to a state highway, the commission is not required to base its speed limit determination solely on the results of the engineering and traffic investigation.

(b) If a local authority requests the department of transportation or an engineer, as provided in subsection (1)(c)(i), to conduct an engineering and traffic investigation based on the belief that a speed limit on a highway under the jurisdiction of the department of transportation is greater than is reasonable or safe, the commission may not increase the speed limit under consideration as a result of the investigation.

(c) (i) A local authority may request at its own expense that an engineering and traffic investigation be completed by a licensed professional engineer selected from a list compiled and approved by a committee as provided in subsection (1)(c)(ii).

(ii) A committee containing two department of transportation staff appointed by the director and two representatives of associations whose membership comprises cities, towns, and counties, as authorized by 7-5-2141 and 7-5-4141, shall review credentials submitted by licensed professional engineers and shall determine who appears on the list of individuals authorized to conduct engineering and traffic investigations for local governments. The list must be updated every 2 years.

(iii) Upon completion of an engineering and traffic investigation conducted for a local government, the department of transportation shall submit a report to the commission with findings and recommendations. The commission shall decide on an appropriate speed limit based on the traffic investigation within 120 days from the date the investigation is submitted to the department of transportation.

(d) A local authority may request a temporary special reduced or increased speed zone for a route or route segment that is under consideration for a reduced or increased speed limit under subsection (1)(a), (1)(b), or (1)(c). If a local authority makes multiple requests for temporary special reduced or increased speed zones, the local authority shall prioritize the requests. The department of transportation shall conduct a preliminary visual and engineering review of a route or a route segment for which a temporary special speed zone is requested. The reviewing party must include a representative of the local authority. Upon completion of the preliminary review, if the department of transportation concurs with the local authority that a temporary special reduced or increased speed limit is warranted, a temporary special reduced or increased speed zone may be established upon formal approval by the commission. The temporary special reduced or increased speed limit remains in effect until a complete traffic and engineering study has been done on the route or route segment and the commission has made a determination on changing the speed limit.

(2) The department Pending completion of transportation shall erect an engineering and maintain appropriate signs giving notice of special limits. When traffic investigation as provided the for signs are erected, in subsection (1), the limits are effective for those zones at all times or at other times that the commission sets. may temporarily set a speed limit of not less than 75 miles an hour on a segment of an interstate highway that it reasonably believes is not suitable for the limit

(3) The authority department of the commission under this section includes the authority to set reduced nighttime speed limits on transportation shall erect curves and other dangerous locations. maintain appropriate signs giving notice of special limits. If the special limits apply to a school zone, the department shall consider the use of electronic signs in lieu of or in addition to other appropriate signs. When the signs are erected, the limits are effective for those zones at all times or at other times that the commission sets.

(4) This The authority of section the does not authorize the commission commission to set a statewide speed limit.

(a) to set reduced nighttime speed limits on curves and other dangerous locations; and

(b) to reassess and reset speed limits set by the transportation commission pursuant to this section.

(5) This section does not authorize the commission to set a statewide speed limit.

(6) (a) The violation of a speed limit established under this section, except subsection (2), is a misdemeanor offense and is punishable as provided in 61-8-711.

(b) The violation of a speed limit established under subsection (2) is punishable as provided in 61-8-725.

Establishment of special speed zones and temporary special reduced speed limits – engineering and traffic investigation