The Standard Traffic Ordinance as adopted is hereby modified by adding thereto the following: The maximum lawful speed limit shall be 20 miles per hour on the following described portions of streets and avenues within the city:
(a) Second Street from Ohio Street west to Missouri Street.
(b) First Street from Ohio Street west to Missouri Street.
(c) Ohio Street from Second Street south the ending of Ohio Street.
(d) The first alley west of Ohio Street at Second Street south to the ending of the alley.
Appropriate signs shall be erected at any speed zone which alters the standard speed zones set forth in Section 33 of the Standard Traffic Ordinance as adopted by the city. (Ord. 360, Sec. 1)