All road plans, plats and field notes and true and accurate diagrams of water, sewage and electric power lines for rural subdivisions shall be filed with and approved by the board of supervisors and the county engineer before the subdivision is laid out or recorded. Such plans shall be clearly designated as “completed”, “partially completed” or “proposed” with a statement of the portion completed and the expected date of full completion. If such road plans are not approved as provided in this section such roads shall not become the part of any road system as defined in this chapter.