12.52.040: LOCATIONS FOR PASSENGERS:
No person shall ride, and no driver of a motor vehicle shall knowingly permit any person to ride, upon any portion of any vehicle not designed or intended for the use of passengers. This provision shall not apply to any vehicle driven elsewhere than upon a street, or to an employee engaged in the necessary discharge of his or her duty, or to persons riding entirely within or upon any motor vehicle in space intended for any load on such vehicle. (Prior code title 46, art. 15 § 227)