Whenever a rural arterial enters a city or town, the proper city or town and county officials shall jointly plan the improvement of the arterial in their respective long-range plans. Whenever a rural arterial connects with and will be substantially affected by a programmed construction project on a state highway, the proper county officials shall jointly plan the development of such arterial with the department of transportation district administrator. The board shall adopt rules encouraging the system development of county-city arterials in rural areas and rural arterials with state highways.