Whenever engineering and traffic investigations indicate that the state speed permitted at an intersection is greater than is reasonable or safe under the conditions found to exist at such an intersection, the legislative authority of the City, subject to the approval of the state highway commission in cases involving state highways, shall determine and declare a reasonable and safe speed limit thereat, which shall be effective at all times or during hours of daylight or darkness or at such other times as may be determined; provided, that appropriate signs giving notice thereof are erected at the intersection or upon the approaches thereto. (Ord. 304 § 36, 1963).