A person propelling a bicycle shall not ride other than astride a permanent and regular seat attached thereto. No bicycle shall be used to carry more persons at one time than the number for which it is designed and equipped. It is unlawful for the operator of any bicycle (or of any motorcycle not equipped with a side car or built to transport two persons), when upon any public street, to carry any other person upon the handlebars, frame, or other part thereof, or for any other person to so ride on such vehicle. This section does not apply to the use of a bicycle in a parade or special event authorized by the City.
(Code of Iowa, Sec. 321.234[3 and 4])