California Code, Vehicle Code - VEH § 21057

Every police and traffic officer is hereby expressly prohibited from using a siren or driving at an illegal speed when serving as an escort of any vehicle, except when the escort or conveyance is furnished for the preservation of life or when expediting movements of supplies and personnel forany federal, state, or local governmental agency during a national emergency, or state of war emergency, or state of emergency, or local emergency as defined in Section 8558 of the Government Code.