It shall be unlawful for any person to make any U-turn at any street intersection or on any street or alley within the business district of the city, nor shall any vehicle be turned so as to proceed in the opposite direction upon any curve or upon the approach to or near the crest of a grade, where such vehicle cannot be seen by the driver of any other vehicle approaching from either direction within five hundred feet (500'). (1977 Code § 8-1-4)