Iowa Code Title VIII. Transportation [Chs. 306-330B] § 321.343. Certain vehicles must stop

1. The driver of a motor vehicle carrying passengers for hire, a school bus, or a vehicle carrying hazardous material and required to stop before driving across a railroad track by motor carrier safety rules adopted under section 321.449, before driving across at grade any track of a railroad, shall stop the vehicle within fifty feet but not less than fifteen feet from the nearest rail. While stopped, the driver shall listen and look in both directions for an approaching railroad train or railroad track equipment, and for signals indicating the approach of a railroad train or railroad track equipment, and shall not proceed until the driver can do so safely.

2. The driver of a commercial motor vehicle shall comply with all of the following provisions that apply to the driver:

3. No stop need be made at a crossing where a peace officer or a traffic-control device directs traffic to proceed. No stop need be made at a crossing designated by an “exempt” sign. An “exempt” sign shall be posted only where the tracks have been partially removed on either side of the roadway.