Cal. Pub. Util. Code § 7533
The board of directors of any railroad corporation may at any time after the original location and construction of its railroad, in order to provide better facilities for the public service, construct an additional main line track or tracks either adjacent to the located and operated line or otherwise, but always in whole or in part between the same termini. The railroad corporation may, without abandoning the original location, acquire such rights of way as are necessary for the additional track or tracks, with their appendages and adjuncts, of a similar width as provided in Section 7526 for the original location, either by purchase or condemnation, as therein provided, and may operate the additional tracks in conjunction with any tracks previously constructed, as additional facilities for the railroad system. Nothing herein supersedes or repeals any law relating to the regulation of railroad corporations by the commission, or any law requiring railroads to obtain franchises from the cities or counties through which the additional tracks may pass.
Ca. Pub. Util. Code § 7533