California Code, Health and Safety Code - HSC § 33448

In a county with a population of 4,000,000 persons or more, or in a city of 500,000 persons or more, an agency may, with the consent of the legislative body, acquire, construct, and finance by the issuance of bonds or otherwise a public improvement whether within or without a project area consisting of a transportation collection and distribution system and peripheral parking structures and facilities, including sites therefor, to serve the project area and surrounding areas, upon a determination by resolution of the agency and the legislative body that such public improvement is of benefit to the project area.  Such determination by the agency and the legislative body shall be final and conclusive as to the issue of benefit to the project area.

The agency shall, in order to exercise the powers granted by this section, enter into an agreement with the rapid transit district which includes the county or city, or a portion thereof, in which agreement the rapid transit district shall be given all of the following responsibilities: