Iowa Code § 321.438: Windshields and windows.

1. A person shall not drive a motor vehicle equipped with a windshield, sidewings, or side or rear windows which do not permit clear vision.

2. A person shall not operate on the highway a motor vehicle equipped with a front windshield, a side window to the immediate right or left of the driver, or a sidewing forward of and to the left or right of the driver which is excessively dark or reflective so that it is difficult for a person outside the motor vehicle to see into the motor vehicle through the windshield, window, or sidewing.

a. The department shall adopt rules establishing a minimum measurable standard of transparency which shall apply to violations of this subsection.

b. This subsection does not apply to a person who operates a motor vehicle owned or leased by a federal, state, or local law enforcement agency if the operation is part of the person’s official duties.

3. Every motor vehicle except a motorcycle, or a vehicle included in the provisions of section 321.383 or section 321.115 shall be equipped with a windshield in accordance with section 321.444.