This is a violation of Iowa Code 321.288 which states:
321.288 CONTROL OF VEHICLE -- REDUCED SPEED.
A person operating a motor vehicle shall have the vehicle under control at all times and shall reduce the speed to a reasonable and proper rate:
1. When approaching and passing a person walking in the traveled portion of the public highway
2. When approaching and passing an animal which is being led, ridden, or driven upon a public highway.
3. When approaching and traversing a crossing or intersection of public highways, or a bridge, sharp turn, curve, or steep descent, in a public highway.
4. When approaching and passing an emergency warning device displayed in accordance with rules adopted under section 321.449, or an emergency vehicle displaying a revolving or flashing light.
5. When approaching and passing a slow moving vehicle displaying a reflective device or alternative reflective device as provided by section 321.383.
6. When approaching and passing through a sign-posted road work zone upon the public highway.