Cal. Sts. & High. Code § 30107

In any such contract or permit, the commission may authorize the transportation company or corporation, district, or political subdivision providing transportation to use the transportation facilities and additional transportation facilities of the commission upon such terms and in such manner as the commission deems proper. Such use may be authorized without restriction to the particular toll bridge or other highway crossing to which the transportation facilities and additional transportation facilities relate, but the use authorized shall be for or in aid of the transportation of persons or property over that bridge or other highway crossing or the approaches thereto.