(a) The commission may enter into an agreement with the commissioners court of a county for the improvement by the county 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 and including drainage facilities, surveying, traffic counts, driveways, landscaping, signs, lights, or guardrails.