Iowa Code § 321E.24: Warning and lighting devices on oversize vehicles and loads.

The department shall adopt rules pursuant to chapter 17A regarding oversize load signs, warning flags, vehicle length warning lights, and projecting-load lights. A vehicle or combination of vehicles with a gross weight or combined gross weight exceeding eighty thousand pounds shall not be required to display warning lights based on the vehicle’s weight, but may otherwise be required to display warning lights based on length, a projecting load, or other factors, as provided by law.