49 CFR §1248.3

1. (a)Commodity codes 01 through 422 and 44 through 462, named in § 1248.101, shall include only carload traffic. All shipments weighing less than 10,000 pounds shall be included in commodity code 431, “Small packaged freight shipments.”
2. (b)A carload for the purpose of this order shall consist of a shipment of not less than 10,000 pounds of one commodity. A mixed carload for the purpose of this order shall be treated as a carload of that commodity which forms the major portion of the shipment in weight. If a single shipment is loaded into more than one car, each car used shall be reported as a carload. If more than one carload shipment is loaded into one car, each shipment shall be reported separately as a carload.