A county may relinquish or transfer jurisdiction over any public highway to a municipality only if: (1) The highway has a pavement condition index minimum rating of 85 or above; or (2) There is mutual agreement between the county and the municipality to transfer jurisdiction of a highway, even though the pavement condition index minimum rating is less than 85. The county must inform the Department of Transportation of a proposed transfer of jurisdiction over a highway. The county may only alter its highway plan by authority of, and in accordance with, a written executive order of the department, pursuant to § 31-12-2. 23 For purposes of this section, "pavement condition index" means a numerical index between 0 and 100 that is used to indicate the general condition of pavement on a section of highway, with higher numbers indicating pavement in better condition. 3