It shall be the duty of the said county engineer or chief engineer of the division of public roads, subject to the approval and direction of the county commission to:
(1) Employ, supervise, and direct such assistants as are necessary to construct and maintain properly the county public roads, highways, and bridges;
(2) Perform such engineering and surveying services as may be required to prepare and maintain the necessary maps, plans, and records;
(3) Maintain the necessary accounting records to reflect the cost of constructing and maintaining the county highway system; and
(4) Perform such other duties as are necessary and incident to the operation of the county highway system as directed by the county commission.