The county road system must be the roads designated and selected by the boards of county commissioners. The director must be informed of the system so designated. Any changes of the original designation which can be justified and based on new developments must be made by the board of county commissioners and the director must be notified of such changes. In designating and selecting roads on the county road system, the boards of county commissioners of the several counties shall take into account such factors as the actual or potential traffic volumes, the conservation and development of the county’s natural resources, the general economy of the communities, and the desirability of integrating such county roads into the general scheme of the statewide network of county roads.