The speed limit on all streets within the incorporated limits of the city shall be twenty-five miles per hour, except as this chapter or Chapter 10.20 of this code, declares and determines upon the basis of engineering and traffic investigation that certain speed limits shall be applicable on specified streets or in certain areas, in which event it shall be unlawful for any person to drive a vehicle at a speed in excess of any speed so declared when signs are in place giving notice thereof. (Ord. 610 § 2, 1988).