Riding on Bicycle
21204. (a) No person operating a bicycle upon a highway shall ride other than upon or astride a permanent and regular seat attached thereto.
(b) No operator shall allow a person riding as a passenger, and no person shall ride as a passenger, on a bicycle upon a highway other than upon or astride a separate seat attached thereto. If the passenger is four years of age or younger, or weighs 40 pounds or less, the seat shall have adequate provision for retaining the passenger in place and for protecting the passenger from the moving parts of the bicycle.