Every person operating a bicycle upon any sidewalk shall operate the bicycle in a careful and prudent manner and at a rate of speed no greater than is reasonable and proper under the conditions existing at the point of operation, taking into account the amount and character of pedestrian traffic, grade and width of sidewalk, and condition of surface; and when because of the width of such sidewalk or the amount of pedestrian traffic thereon, riding a bicycle on such sidewalk would endanger or unreasonably inconvenience pedestrians, such person shall stop and dismount from such bicycle. (1961 code § 11.60.061.)