California Code, Public Utilities Code - PUC § 768

The commission may, after a hearing, require every public utility to construct, maintain, and operate its line, plant, system, equipment, apparatus, tracks, and premises in a manner so as to promote and safeguard the health and safety of its employees, passengers, customers, and the public.  The commission may prescribe, among other things, the installation, use, maintenance, and operation of appropriate safety or other devices or appliances, including interlocking and other protective devices at grade crossings or junctions and block or other systems of signaling.  The commission may establish uniform or other standards of construction and equipment, and require the performance of any other act which the health or safety of its employees, passengers, customers, or the public may demand.  The Department of the California Highway Patrol shall have the primary responsibility for the regulation of the safety of operation of passenger stage corporations.  The commission shall cooperate with the Department of the California Highway Patrol to ensure safe operation of these carriers.