Whenever the City Council shall determine, upon the basis of an engineering and traffic study, that the maximum speed law as provided by section 8-4-1 of this chapter, and any amendments thereto, shall not apply on any streets or parts of streets, the Council may, by motion, instruct the Chief of Police to place appropriate signs on such streets or parts of streets, indicating a different speed, and it shall be unlawful for the driver of any vehicle to exceed the maximum speed thus indicated by such signs. (1975 Code § 8-4-2)