In the selection of the mileage of road to be designated in each county for inclusion in the major collector road system consideration shall be given to the inclusion of principal county and township roads so located as to provide adequate intertown and intercounty connections to best serve the rural population of the state. The determination of the mileage to be included in the major collector road system shall be based on factual data obtained by the county commissioners and the secretary of transportation, cooperating with the federal government in accordance with title 23 of the code of federal regulations.

The designation of the road mileage to be included in the major collector road system shall hereafter be the joint responsibility of the boards of county commissioners and the secretary of transportation, the board of county commissioners making the recommendation and the secretary concurring in the recommendation.