Iowa's current motorcycle laws:

321.275 Operation of motorcycles and motorized bicycles.
1. General. The motor vehicle laws apply to the operators of motorcycles and motorized bicycles to the extent practically applicable.
2. Riders.
a. Motorized bicycles. A person operating a motorized bicycle on the highways shall not carry any other person on the vehicle.
b. Motorcycles . A person shall not operate or ride a motorcycle on the highways with another person on the motorcycle unless the motorcycle is designed to carry more than one person. The additional passenger may ride upon the permanent and regular seat if designed for two persons, or upon another seat firmly attached to the motorcycle at the rear of the operator. The motorcycle shall be equipped with footrests for the passenger unless the passenger is riding in a sidecar or enclosed cab. The motorcycle operator shall not carry any person nor shall any other person ride in a position that will interfere with the operation or control of the motorcycle or the view of the operator.
3. Sitting position. A person operating a motorcycle or motorized bicycle shall ride only upon the vehicle's permanent and regular attached seat. Every person riding upon the vehicle shall be sitting astride the seat, facing forward with one leg on either side of the vehicle.
4. Use of traffic lanes. Persons shall not operate motorcycles or motorized bicycles more than two abreast in a single lane. Except for persons operating such vehicles two abreast, a motor vehicle shall not be operated in a manner depriving a motorcycle or motorized bicycle operator of the full use of a lane. A motorcycle or motorized bicycle shall not be operated between lanes of traffic or between adjacent lines or rows of vehicles. The operator of a motorcycle or motorized bicycle shall not overtake and pass in the same lane occupied by the vehicle being overtaken unless the vehicle being overtaken is a motorcycle or motorized bicycle.
5. Headlights on. A person shall not operate a 1977 or later model year motorcycle or any model year motorized bicycle upon the highways without displaying at least one lighted headlamp of the type described in section 321.409 . However, this subsection is subject to the exceptions with respect to parked vehicles as provided in this chapter.
6. Packages. The operator of a motorcycle or motorized bicycle shall not carry any package, bundle, or other article which prevents the operator from keeping both hands on the handlebars.
7. Parades. The provisions of this section do not apply to motorcycles or motorized bicycles when used in a parade authorized by proper permit from local authorities.
8. Bicycle safety flags required on motorized bicycles. When operated on a highway, a motorized bicycle shall have a bicycle safety flag which extends not less than five feet above the ground attached to the rear of the motorized bicycle. The bicycle safety flag shall be triangular in shape with an area of not less than thirty square inches, and be Day-Glo in color.
[C71, 73, 75, 77, 79, 81, §321.275]
89 Acts, ch 184, §1; 98 Acts, ch 1075, §22; 98 Acts, ch 1178, §3
For applicable scheduled fines, see § 805.8A , subsection 6, paragraph b, and subsection 9