(1) If the county road commission, the township board, and the department of state police unanimously determine upon the basis of an engineering and traffic investigation that the speed of vehicular traffic on a county highway is greater or less than is reasonable or safe under the conditions found to exist upon any part of the highway, then acting unanimously they may establish a reasonable and safe maximum or minimum speed limit on that county highway that is effective at the times determined when appropriate signs giving notice of the speed limit are erected on the highway. A township board may petition the county road commission or the department of state police for a proposed change in the speed limit. A township board that does not wish to continue as part of the process provided by this subsection shall notify in writing the county road commission. A public record of a traffic control order establishing a modified speed limit authorized under this subsection must be filed at the office of the county clerk of the county in which the limited access freeway or state trunk line highway is located, and a certified copy of a traffic control order is evidence in every court of this state of the authority for the issuance of that traffic control order. As used in this subsection, "county road commission" means the board of county road commissioners elected or appointed under section 6 of chapter IV of 1909 PA 283, MCL 224.6, or, in the case of a charter county with a population of 1,500,000 or more with an elected county executive that does not have a board of county road commissioners, the county executive.

    (2) In the case of a county highway, a township board may petition the county road commission, or in counties where there is no road commission but there is a county board of commissioners, the township board may petition the county board of commissioners for any of the following:

    (a) A proposed change in the speed limit without the necessity of a speed study consistent with the methods prescribed for establishing speed limits under section 627.

    (b) A proposed change in the speed limit consistent with the provisions for establishing speed limits under this section.

    (c) The posting of an advisory sign or device for the purpose of drawing the attention of vehicle operators to an unexpected condition on or near the roadway that is not readily apparent to road users.

    (3) The state transportation department and the department of state police shall jointly determine any modified maximum or minimum speed limits on limited access freeways or trunk line highways consistent with the requirements of this section. A public record of a traffic control order establishing a modified speed limit authorized under this subsection must be filed at the office of the county clerk of the county in which the limited access freeway or trunk line highway is located, and a certified copy of a traffic control order is evidence in every court of this state of the authority for the issuance of that traffic control order.

    (4) A local road authority shall determine any modified speed limits on local highways consistent with the requirements of this section. A public record of a traffic control order establishing a modified speed limit authorized under this subsection must be filed at the office of the city or village or administrative office of the airport, college, or university in which the local highway is located, and a certified copy of the traffic control order is evidence in every court of this state of the authority for the issuance of that traffic control order.

    (5) A speed limit established under this section must be determined in accordance with traffic engineering practices that provide an objective analysis of the characteristics of the highway and by the eighty-fifth percentile speed of free-flowing traffic under ideal conditions on the fastest portion of the highway segment for which the speed limit is being posted. The speed limit must be in multiples of 5 miles per hour and rounded to a multiple that is within 5 miles per hour of the eighty-fifth percentile speed. A speed limit established under this section may be set below the eighty-fifth percentile speed if an engineering and safety study demonstrates a situation with hazards to public safety that are not reflected by the eighty-fifth percentile speed, but must not be set below the fiftieth percentile speed.

    (6) If a highway segment includes 1 or more features with a design speed that is lower than the speed limit determined under subsection (5), the road authority may post advisory signs.

    (7) If upon investigation the state transportation department or county road commission and the department of state police find it in the interest of public safety, they may order township, city, or village officials to erect and maintain, take down, or regulate the speed limit signs, signals, or devices as directed, and in default of an order the state transportation department or county road commission may cause the designated signs, signals, and devices to be erected and maintained, taken down, regulated, or controlled, in the manner previously directed, and pay for the erecting and maintenance, removal, regulation, or control of the sign, signal, or device out of the highway fund designated.

    (8) Signs posted under this section must conform to the Michigan manual on uniform traffic control devices.

    (9) An individual who violates a speed limit established under this section is responsible for a civil infraction.

    (10) As used in subsections (2) to (9), "county road commission" means any of the following:

    (a) The board of county road commissioners elected or appointed under section 6 of chapter IV of 1909 PA 283, MCL 224.6.

    (b) In the case of the dissolution of the county road commission under section 6 of chapter IV of 1909 PA 283, MCL 224.6, the county board of commissioners.

    (c) In the case of a charter county with a population of 1,500,000 or more with an elected county executive that does not have a board of county road commissioners, the county executive.

    (d) In the case of a charter county with a population of more than 750,000 but less than 1,000,000 with an elected county executive that does not have a board of county road commissioners, the department of roads.

    (11) As used in this section:

    (a) "Design speed" means that term as used and determined under "A Policy on Geometric Design of Highways and Streets", seventh ed., 2018, issued by the American Association of State Highway and Transportation Officials.

    (b) "Local road authority" means the governing body of a city, village, airport, college, or university.

    (c) "Traffic control order" means a document filed with the proper authority that establishes the legal and enforceable speed limit for the highway segment described in the document.