27400. No person operating any motor vehicle or bicycle shall wear any headset covering, or any earplugs in, both ears. The prohibition of this section does not apply to any of the following: (a) Persons operating authorized emergency vehicles, as defined in Section 165. (b) Any person engaged in the operation of either special construction equipment or equipment for use in the maintenance of any highway. (c) Any person engaged in the operation of refuse collection equipment who is wearing a safety headset or safety earplugs. (d) Any person wearing personal hearing protectors in the form of custom earplugs or molds that are designed to attenuate injurious noise levels. The custom plugs or molds shall be designed in a manner so as to not inhibit the wearer's ability to hear a siren or horn from an emergency vehicle or a horn from another motor vehicle. (e) Any person using a prosthetic device which aids the hard of hearing.