The State traffic laws regulating the speed of vehicles shall be applicable upon all streets within this City except as altered by the Council of the City of Phoenix and set forth in schedule I, section 36-158, as authorized by State law, in which event it shall be prima facie unlawful for any person to drive a vehicle at a speed in excess of any speed so declared in schedule I when signs are in place giving notice thereof. (Code 1962, § 37-20.01; Ord. No. G-937)