Per 49 CFR, when transporting a placarded load of hazardous materials, the driver must stop the vehicle within 50 feet but not less than 15 feet from the nearest rail of every railroad-highway grade crossing and check for approaching trains, EXCEPT when:

1. The grade crossing is in a business district
2. The crossing is controlled by a police officer or a flagman, or it is an abandoned/exempt crossing
3. The vehicle is empty of cargo
4. The driver is running ahead of schedule