Iowa Code Title VIII. Transportation [Chs. 306-330B] § 321.290. Special restrictions

1. Whenever the department shall determine upon the basis of an engineering and traffic investigation that any speed limit set forth in this chapter is greater or less than is reasonable or safe under the conditions found to exist at any intersection or other place or upon any part of the primary road system or upon any part of a primary road extension, the department shall determine and declare a reasonable and safe speed limit which shall be effective when appropriate signs giving notice of the speed limit are erected at such intersection or other place or part of the highway.

2. Whenever the council in any city shall determine upon the basis of an engineering and traffic investigation that any speed limit set forth in this chapter is greater or less than is reasonable or safe under the conditions found to exist at any intersection or other place or upon any part of the city street system, except primary road extensions, said council shall determine and adopt by ordinance such higher or lower speed limit as it deems reasonable and safe. Such speed limit shall be effective when proper and appropriate signs giving notice of the speed limit are erected at such intersections or other place or part of the street.