(a) Improvement of the state highway system with federal aid shall be made under the exclusive and direct control of the department and with appropriations made by the legislature out of the state highway fund.
(b) The department may improve the state highway system without federal aid either with or without county aid. Improvements made without federal aid must comply with Section 223.045.
(c) The department shall make or prepare any survey, plan, specifications, or estimate for an improvement of the state highway system if any part of the improvement will be made with federal aid.
(d) The commissioners court of a county may not directly control the making of an improvement of the state highway system unless the plan and specifications for the improvement have been approved by the director.