ASSOCIATION OF AMERICAN RAILROADS
Circular OT-55
Effective May 1st. 2019
"Key Trains"
A. Definition: A “Key Train” is any train with:
• One tank car load of Poison or Toxic Inhalation Hazard1 (PIH or TIH) (Hazard Zone A,
B, C, or D), anhydrous ammonia (UN1005), or ammonia solutions (UN3318), or;
• 20 car loads or intermodal portable tank loads of any combination of hazardous material,
or;
• One or more car loads of Spent Nuclear Fuel (SNF), High Level Radioactive Waste
(HLRW).