Iowa Code § 327F.31
An ordinance or resolution adopted by a political subdivision of this state which relates to the speed of a train in an area within the jurisdiction of the political subdivision is subject to approval by the state department of transportation. Any speed ordinance or resolution adopted by a political subdivision of the state prior to July 1, 1988, which has not been approved by the department shall be referred to the department by the political subdivision and shall be in full force and effect upon approval of the ordinance or resolution by the department. This section does not abrogate, modify, or alter any historical or contractual agreement between a political subdivision of the state and a railroad corporation in existence on July 1, 1975.
Iowa Code § 327F.31