Cal. Pub. Util. Code § 100165

The VTA may enter into agreements for the joint use of any property and rights by the VTA and any public agency or public utility operating transit facilities; may enter into agreements with any public agency or public utility operating any transit facilities, and wholly or partially within or without the boundaries of the VTA, for the joint use of any property of the VTA or of the public agency or public utility, or the establishment of through routes, joint fares, transfer of passengers, or pooling arrangements.