California Code, Vehicle Code - VEH § 21367

(a) As provided in Section 125 of the Streets and Highways Code and in Section 21100 of this code, respectively, the duly authorized representative of the Department of Transportation or local authorities, with respect to highways under their respective jurisdictions, including, but not limited to, persons contracting to perform construction, maintenance, or repair of a highway, may, with the approval of the department or local authority, as the case may be, and while engaged in the performance of that work, restrict the use of, and regulate the movement of traffic through or around, the affected area whenever the traffic would endanger the safety of workers or the work would interfere with or endanger the movement of traffic through the area. Traffic may be regulated by warning signs, lights, appropriate control devices, or by a person or persons controlling and directing the flow of traffic.

(b) It is unlawful to disobey the instructions of a person controlling and directing traffic pursuant to subdivision (a).

(c) It is unlawful to fail to comply with the directions of warning signs, lights, or other control devices provided for the regulation of traffic pursuant to subdivision (a).