It shall be the duty of the Transportation Commission to have the Transportation Department construct, reconstruct and maintain, at the cost and expense of the state, all highways under its jurisdiction up to such standards and specifications and with such surfacing material as the Transportation Commission may determine, such paving to be done for each project as rapidly as funds are made available therefor and, as nearly as practicable, immediately upon the completion of all work performed pursuant to grade, drainage and bridge contracts for the project. Such paving shall be done in the order of the relative use and importance of said highways, as may be determined by the present and future traffic censuses thereof and other criteria, taking into consideration their present and future use, convenience, public necessity, public safety, the recorded maintenance expense, and their availability as highways through the state. The type of the paving and surfacing of such highways shall be determined by the executive director, subject to the rules, regulations and orders of the commission as spread on its minutes, after a complete study of the traffic requirements based upon the present and future traffic censuses, taking into consideration the factors above set forth. However, no highways shall be constructed, reconstructed, or maintained out of any patented paving material, regardless of what kind, on which a direct royalty is paid by the commission or any contractor; and the commission shall not have included in the plans or specifications for constructing, reconstructing, or maintenance of any highway the requirements that any material used or specified shall be laid under any process patented requiring the payment of a direct royalty for use of such process or patent.