(a) The commissioners court of a county may enter into an agreement with the commission for the county to carry out a project or activity for the improvement of a segment of the state highway system.
(b) In this section, "improvement" means construction, reconstruction, maintenance, and the making of a necessary plan or survey before beginning construction, reconstruction, or maintenance and includes a project or activity appurtenant to a state highway, including surveying, making a traffic count, or landscaping or an activity relating to a drainage facility, driveway, sign, light, or guardrail.