Unlawful speed.

(1) No person shall drive a vehicle on a highway at a speed greater than is reasonable and prudent under the conditions and having regard to the actual and potential hazards then existing. In every event, speed shall be controlled as may be necessary to avoid colliding with any person, vehicle, or other conveyance or object on or entering the highway in compliance with legal requirements and the duty of all persons to use due care.

(2) On all streets or highways, the maximum speed limits for all vehicles must be 30 miles per hour in business or residence districts, and 55 miles per hour at any time at all other locations. However, with respect to a residence district, a county or municipality may set a maximum speed limit of 20 or 25 miles per hour on local streets and highways after an investigation determines that such a limit is reasonable. It is not necessary to conduct a separate investigation for each residence district. The minimum speed limit on all highways that comprise a part of the National System of Interstate and Defense Highways and have not fewer than four lanes is 40 miles per hour, except that when the posted speed limit is 70 miles per hour, the minimum speed limit is 50 miles per hour.

(3) A school bus may not exceed the posted speed limits at any time.

(4) The driver of every vehicle shall, consistent with the requirements of subsection (1), drive at an appropriately reduced speed when:

(a) Approaching and crossing an intersection or railway grade crossing;

(b) Approaching and going around a curve;

(c) Approaching a hill crest;

(d) Traveling upon any narrow or winding roadway; and

(e) Any special hazard exists with respect to pedestrians or other traffic or by reason of weather or highway conditions.

(5) No person shall drive a motor vehicle at such a slow speed as to impede or block the normal and reasonable movement of traffic, except when reduced speed is necessary for safe operation or in compliance with law.

(6) No driver of a vehicle shall exceed the posted maximum speed limit in a work zone area.

(7) A violation of this section is a noncriminal traffic infraction, punishable as a moving violation as provided in chapter 318.