(a) Only the legislature may authorize a project.
(b) A legislative appropriation for a project is directly to a using agency unless the project is to be constructed by the commission, in which event the appropriation is to the commission.
(c) An appropriation for the construction of a project expresses the legislative intent that the project be completed within the limits of the appropriation.
(d) If the legislative authorization provides for stage construction of a project, the commission shall proceed with the project through the specifically authorized stage.