The Standard Carrier Alpha Code (SCAC) is a unique two-to-four-letter code used to identify transportation companies. NMFTA developed the SCAC identification codes in the mid 1960's to facilitate computerization in the transportation industry.

The Standard Carrier Alpha Code is the recognized transportation company identification code used in the American National Standards Institute (ANSI) Accredited Standards Committee (ASC) X12 and United Nations EDIFACT approved electronic data interchange (EDI) transaction sets such as the 856 Advance Ship Notice, the 850 Purchase Order and all motor, rail and water carrier transactions where carrier identification is required. The SCAC is required on tariffs filed with the Surface Transportation Board (STB). The United States Bureau of Customs and Border Protection has mandated the use of the SCAC for their Automated Manifest (AMS) and Pre-Arrival Processing (PAPS) Systems. SCACs are required when doing business with all U.S. Government agencies and with many commercial shippers including, but not limited to, those in the automobile, petroleum, forest products, and chemical industries as well as suppliers to retail businesses and carriers engaged in railroad piggyback trailer and ocean container drayage. Carriers who use the Uniform Intermodal Interchange Agreement (UIIA) are required to maintain a valid SCAC. The petroleum industry uses SCACs in their integrated software programs that expedite the movement of bills of lading, pipeline tickets, product transfer orders, and inventory data. Many commercial shippers and receivers utilize SCACs in their freight bill audit and payment systems.

Certain groups of SCACs are reserved for specific purposes. Codes ending with the letter "U" are reserved for the identification of freight containers. Codes ending with the letter "X" are reserved for the identification of privately owned railroad cars. Codes ending with the letter "Z" are reserved for the identification of truck chassis and trailers used in intermodal service.