The director of transportation shall maintain a laboratory of research and tests and employ qualified personnel to conduct research pertaining to materials, supplies, and equipment used in road construction and maintenance and to test materials, supplies, and equipment used in the construction and maintenance of the state highway system. The director may make tests of road building materials for authorities of any county, municipal corporation, township, or other subdivision of the state. When the director makes such tests he shall collect from such county, municipal corporation, township, or other subdivision of the state a fee sufficient to cover the actual cost of making such tests. The fees collected shall be paid into the state treasury to the credit of the state highway operating fund.