Standard Carrier Alpha Codes were developed in the 1960s. The National Motor Freight Traffic Association developed SCAC codes to computerize the records and data used by the transportation industry.
SCAC codes are unique codes comprised of two, three or four letters assigned to transportation companies for identification freight carriers that are active in the Uniform Intermodal Interchange Agreement ocean carriers, and shipping documents such as purchase orders, packing lists and bills. SCAC codes are classified by the last letter of the code. Codes ending in a 'U' are assigned to freight containers. Codes ending in 'X' are assigned to private railroad cars. Codes that end in the letter 'Z' are assigned to intermodal serviced truck chassis and trailers. A directory of the SCAC codes is issued every year and updated every quarter.