It is unlawful for any person driving or operating, propelling, or causing to be propelled, any vehicle, to fail to stop at the nearest side of the crosswalk where any signal device, school crossing guard, or school safety patrol officer is stationed, giving warning that persons are about to or are crossing the street, and it is further declared unlawful to proceed until the signal device, school crossing guard, or school safety patrol officer indicates that it is proper to proceed. (Prior code § 25.01.009)