The commissioners of each county may appoint and employ a county director of highways, who shall be a person qualified in highway administration, construction and maintenance, to handle the technical and administrative phases of county highway construction, maintenance and improvement. The salary and compensation of the county director of highways shall be fixed by the commissioners and shall be paid from the county highway fund. The county engineer may be appointed as the director of highways if the commissioners so determine; and in that event, his compensation as director of highways shall be distinct from, and in addition to, his compensation as county engineer.