When any county road within the state, which shall have been designated as a part of the federal aid secondary highway system, is brought to standard grade and drain by the county in accordance with plans and specifications approved by the Commission, and where sufficient right-of-way is provided by the county wherein the road is located, and where state and federal funds are available, such road shall be hard surfaced by the Department.
Okla. Stat. tit. 69, § 638