| 1 | A | Alton R.R. | 1/1943-7/1954 | NAKINA | |
| 2 | A | Alton R.R. | Jan-52 | NRHS | |
| 3 | A | ALTON RAILROAD | PWRC | ||
| 4 | A | Alton Railroad | RSRV | ||
| 5 | A&BB | Akron & Barberton Belt R.R. | 7/1923-4/1938 | NAKINA | |
| 6 | A&BB | Akron & Barberton Belt R.R. | 7/23-4/38 | NRHS | |
| 7 | A&BB | AKRON & BARBERTON BELT RAILROAD | PWRC | ||
| 8 | A&BC | ALTOONA & BEECH CREEK RAILROAD | PWRC | ||
| 9 | A&E | ALTON AND EASTERN RAILROAD | PWRC | ||
| 10 | A&ER | ANNAPOLIS & ELK RIDGE RAILROAD | PWRC | ||
| 11 | A&GW | The Alberta & Great Waterways Ry. Co. (Northern Alberta Rys. Co.) | 7/1930-7/1936 | NAKINA | |
| 12 | A&GW | THE ALBERTA & GREAT WATERWAYS RY. CO. (NORTHERN ALBERTA RYS. CO.) | PWRC | ||
| 13 | A&K | ALLEGHANY AND KINZUA RAILROAD | PWRC | ||
| 14 | A&LM | Arkansas & Louisiana Missouri Ry. Co. (Huttig, Mansfield & Nacogdoches R.R.) | 7/1930 | NAKINA | |
| 15 | A&LM | Arkansas & Louisiana Missouri Ry. Co. | 7/1923 & 7/1932-7/1936 | NAKINA | |
| 16 | A&LM | The Arkansas & Louisiana Midland Ry. Co. | 8/1920 | NAKINA | |
| 17 | A&LM | Arkansas & Louisiana Missouri Ry. Co. | 23-Jul | NRHS | |
| 18 | A&LM | *THE ARKANSAS & LOUISIANA MIDLAND RY. CO. | PWRC | ||
| 19 | A&LM | *ARKANSAS & LOUISIANA MISSOURI RY. CO. {HUTTIG, MANSFIELD & NACOGDOCHES RAILROAD] | PWRC | ||
| 20 | A&M | Alabama & Mississippi R.R. Co. | 8/1920 | NAKINA | |
| 21 | A&M | ALABAMA & MISSISSIPPI RAILROAD CO. | PWRC | ||
| 22 | A&NE | ABBOTSFORD & NORTH EASTERN RR | PWRC | ||
| 23 | A&S | Missouri Pacific System | eliminated 1/1979 | NAKINA | |
| 24 | A&S | Abilene & Southern Ry. Co. | 8/1920-7/1954 | NAKINA | |
| 25 | A&S | Abilene & Southern Ry. Co. | 7/23-1/52 | NRHS | |
| 26 | A&S | Missouri Pacific System | eliminated 1/79 | NRHS | |
| 27 | A&S | ABILENE & SOUTHERN RY. CO. | PWRC | ||
| 28 | A&SA | Atlanta & St. Andrews Bay Ry. | 7/1923-1/1952 | NAKINA | |
| 29 | A&SA | Atlanta & St. Andrews Bay Ry. | 7/23-1/52 | NRHS | |
| 30 | A&SA | ATLANTA & ST. ANDREWS BAY RY. CO. | PWRC | ||
| 31 | A&SL | ADIRONDACK & ST LAWRENCE RR | PWRC | ||
| 32 | A&V | The Alabama and Vicksburg Ry. Co. | 7/1923 | NAKINA | |
| 33 | A&V | The Alabama and Vicksburg Ry. Co. (Illinois Central System) | 7/1930 | NAKINA | |
| 34 | A&V | The Alabama and Vicksburg Ry. Co. (Illinois Central R.R. Co.) | 7/1932 | NAKINA | |
| 35 | A&V | The Alabama and Vicksburg Ry. Co. | 23-Jul | NRHS | |
| 36 | A&V | ILLINOIS CENTRAL RR [ALABAMA & VICKSBURG RY. CO.} | PWRC | ||
| 37 | A&W | Alexandria & Western Ry. Co. | 8/1920-7/1923 | NAKINA | |
| 38 | A&W | Alexandria & Western Ry. Co. | 23-Jul | NRHS | |
| 39 | A&W | ALEXANDRIA & WESTERN RY. CO. | PWRC | ||
| 40 | A&WP | Atlanta & West Point R.R. Co. | 4/1938-10/1966 | NAKINA | |
| 41 | A&WP | Atlanta & West Point R.R. Co. | 4/38-10/66 | NRHS | |
| 42 | A&WP | ATLANTA & WEST POINT RAILROAD CO. | PWRC | ||
| 43 | AA | Ann Arbor R.R. Co. | added 1/1989; 1/1994-7/2005 | NAKINA | |
| 44 | AA | Ann Arbor R.R., Michigan Interstate Ry. Co., Operator-in-Reorganization (W. Clark Durant, Ill, Trustee) | eliminated 1/1989 | NAKINA | |
| 45 | AA | Ann Arbor R.R., Michigan Interstate Ry. Co., Operator-in-Reorganization | added 4/1988 | NAKINA | |
| 46 | AA | Ann Arbor R.R. System, Michigan Interstate Ry. Co., Operator-in-Reorganization | eliminated 4/1988 | NAKINA | |
| 47 | AA | Ann Arbor R.R. Co. | eliminated 1/1978 | NAKINA | |
| 48 | AA | Ann Arbor R.R. System, Michigan Interstate Ry. Co., Operator | added 1/1978; 1/1980-1/1985 | NAKINA | |
| 49 | AA | Ann Arbor R.R. Co. (Owned and leased by the Michigan State Highway Commission) (Consolidated Rail Corp. designated operator) | added 7/1976 | NAKINA | |
| 50 | AA | Ann Arbor R.R. Co., John M. Chase, Jr., Trustee | eliminated 7/1976 | NAKINA | |
| 51 | AA | Ann Arbor R.R. Co. | 7/1932-1/1975 | NAKINA | |
| 52 | AA | Ann Arbor R.R. Co. | 4/38-1/75; eliminated 1/78 | NRHS | |
| 53 | AA | Ann Arbor R.R. System, Michigan Interstate Ry. Co., Operator | added 1/78; 1/80 | NRHS | |
| 54 | AA | Ann Arbor R.R. System, Michigan Interstate Ry. Co., Operator-in-Reorganization | eliminated 4/88 | NRHS | |
| 55 | AA | Ann Arbor R.R., Michigan Interstate Ry. Co., Operator-in-Reorganization | added 4/88 | NRHS | |
| 56 | AA | Ann Arbor R.R., Michigan Interstate Ry. Co., Operator-in-Reorganization (W. Clark Durant, Ill, Trustee) | eliminated 1/89 | NRHS | |
| 57 | AA | Ann Arbor R.R. Co. | added 1/89; 1/94-7/2000 | NRHS | |
| 58 | AA | ANN ARBOR RAILROAD | PWRC | ||
| 59 | AA | Ann Arbor Railroad | RSRV | ||
| 60 | AAA | Ansett Australia | IATA: AN | ICAO1 | |
| 61 | AAA | AAA WAREHOUSE CORPORATION (SHELL OIL PRODUCTS US) | PWRC | ||
| 62 | AAAB | AAA PAPER STOCK CO | SCAC3 | ||
| 63 | AAAB | AAA MOTORS | SCAC4 | ||
| 64 | AAAC | AAACTION TRANSPORTATION INC | SCAC4 | ||
| 65 | AAAD | A A A DELIVERY INC | SCAC3 | ||
| 66 | AAAD | A A A DELIVERY INC | SCAC4 | ||
| 67 | AAAE | AAA TRANSFER & STORAGE INC | SCAC3 | ||
| 68 | AAAG | AAA MOVING & STORAGE CO INC | SCAC3 | ||
| 69 | AAAG | ATC LOGISTICS INC | SCAC4 | ||
| 70 | AAAI | AAA RENT-A-CAR INC | SCAC3 | ||
| 71 | AaAJ | Aabenraa Amts Jernbaner | 1899 - 1926 | DK | jernbanen.dk |
| 72 | AAAJ | AAA VAN SERVICE INC | SCAC3 | ||
| 73 | AAAJ | Aabenraa Amts Jernbaner | 1899 - 1926; 1000 mm | DK | TRAFFIC |
| 74 | AAAL | AAA MOBILE HOME TRANSPORTATION INC | SCAC3 | ||
| 75 | AAAM | AAA MOTOR LINES | SCAC3 | ||
| 76 | AAAN | AAA MOVING AND STORAGE INC | SCAC3 | ||
| 77 | AAAO | AAA AIR EXPRESS | SCAC3 | ||
| 78 | AAAO | AAMODT INC | SCAC4 | ||
| 79 | AAAQ | A-A-ACHEN ADVANTAGE LIMO INC | SCAC3 | ||
| 80 | AAAU | ARGHIRES CONTAINER SHIPPING CO. | SCAC3 | ||
| 81 | AAAU | ASIA CONTAINER LEASING CO LTD | SCAC4 | ||
| 82 | AAAV | AAA ASSOCIATES MOVING & STORAGE | SCAC3 | ||
| 83 | AAAW | AAA WALKER TRANSPORTATION SERVICES | SCAC4 | ||
| 84 | AAAX | Shell Oil Products US (Lubricants) | eliminated 7/2004 | NAKINA | |
| 85 | AAAX | AAA Warehouse Corp. | 1/1994 (not listed) | NAKINA | |
| 86 | AAAX | AAA Warehouse Corp. | Jan-94 | NRHS | |
| 87 | AAAX | AAA WAREHOUSE CORPORATION (SHELL OIL PRODUCTS US) | PWRC | ||
| 88 | AAAX | AAA Warehouse Corporation (Shell Oil) | RSRV | ||
| 89 | AAAY | AAAA FORWARDING INC | SCAC3 | ||
| 90 | AAB | Abelag Aviation | IATA: W9 | ICAO1 | |
| 91 | AABB | A-ABBOT VAN LINES | SCAC3 | ||
| 92 | AABB | AGENCIA ADUANAL BENITO BARRERA | SCAC4 | ||
| 93 | AABD | ANGOLA & BUFFALO DELIVERY | SCAC3 | ||
| 94 | AABE | A & B EXPRESS INC | SCAC3 | ||
| 95 | AABE | ABOVE AND BEYOND CARGO SERVICES INC | SCAC4 | ||
| 96 | AABF | A & A BROKERS INC | SCAC3 | ||
| 97 | AABG | AABLE LOGISTICS INC | SCAC4 | ||
| 98 | AABH | AABALON MOVING SERVICES | SCAC3 | ||
| 99 | AABH | AABALON MOVING SERVICES INC | SCAC4 | ||
| 100 | AABI | AABCO INC | SCAC3 |