California Code, Public Utilities Code - PUC § 130257

The commission may enter into an agreement with the Department of Transportation for the department to provide those services which are within the capabilities of the department to effectively perform in connection with the development and construction of any approved exclusive public mass transit guideway system or rapid transit system.

The commission shall retain final authority to decide those matters for which it is responsible by law pertaining to the planning, design, construction, and operation of any exclusive public mass transit guideway system or rapid transit system.

The department shall perform such services agreed upon in accordance with the law and regulations that are applicable to the commission and the department.