Sts. & Hy. Code, § 560.1

Upon the completion of the additional subterranean tube between the Cities of Oakland and Alameda, in the vicinity of Webster Street, to be used in connection with the Posey Tube, both of which tubes are included in the description of Route 260, the department may by executive order, rule or regulation, designate both of said tubes, and the approaches leading to or from the nearest state highway or city street, as one-way highways, and thereafter restrict said tubes and approaches to one-way traffic, proceeding in opposite directions as to each other. Upon the placing of signs notifying the public of such restrictions, any person who willfully fails to observe such sign is guilty of a misdemeanor.