Common carriers (operating railroads)
A Alton RailroadAA Ann Arbor Railroad (1895-1976) → Ann Arbor Railroad (1988)A&A Anniston and Atlantic RailroadAAR Association of American RailroadsAB Akron Barberton Cluster RailwayABB Akron and Barberton Belt RailroadABCKAlaska British Columbia Transportation CompanyABECAberdeen Electric CompanyABL Alameda Belt LineABM Texas and Pacific Railway → Missouri Pacific RailroadABN Alabama Northern Railway → Ashland RailwayABPRAberdeen and Briar Patch Railway → Aberdeen, Carolina and Western RailwayABR Athens LineABS Alabama Southern RailroadAC Algoma Central and Hudson Bay Railway → Algoma Central RailwayACBLAmerican Commercial Barge LinesACISAlgoma Central RailwayACJRAshtabula, Carson and Jefferson RailroadACL Atlantic Coast Line Railroad → Seaboard Coast Line Railroad → Seaboard System Railroad → CSX TransportationACRCAndalusia and Conecuh RailroadACWRAberdeen, Carolina and Western RailwayACY Akron, Canton and Youngstown Railroad → Norfolk and Western Railway → Norfolk Southern RailwayAD Atlantic and Danville Railway → Norfolk, Franklin and Danville RailwayADBFAdrian and Blissfield RailroadADIRAdirondack RailwayADN Ashley, Drew and Northern Railway → Arkansas, Louisiana and Mississippi RailroadAE Arizona Eastern RailroadAEC Atlantic and East Carolina RailwayAEFRAurora, Elgin and Fox River ElectricAER Algoma Eastern RailwayAERCAlbany and Eastern RailroadAF Alabama and Florida RailwayAFLRAlabama and Florida RailroadAG Abbeville-Grimes Railway → A&G Railroad → Bay Line RailroadAGCRAlamo Gulf Coast RailroadAGE Albertson Great Eastern RailroadAGLFAtlantic and Gulf Railroad → Knoxville and Holston River RailroadAGR Alabama and Gulf Coast RailwayAGRDA&G RailroadAGS Alabama Great Southern RailroadAlberta and Great Waterways RailwayAHMRArlington Heights Motor RailwayAHGXAmerican Heritage GirlsAHT Alaska Hydro-TrainAHW Ahnapee and Western Railway → Fox Valley and Western Ltd.AIRIAlabama Industrial RailroadAJ Alma and Jonquieres RailwayAJR Artemus-Jellico RailroadAKC Arkansas Central RailroadAKDNAcadiana RailwayAKMDArkansas Midland RailroadAL Almanor RailroadALABAlabama RailroadArkansas, Louisiana and Gulf RailwayALLN Allentown and Auburn RailroadALM Arkansas and Louisiana Midland Railway → Arkansas and Louisiana Missouri Railway → Arkansas, Louisiana and Mississippi RailroadALQSAliquippa and Southern RailroadALS Alton and Southern Railroad → Alton and Southern RailwayALT Airlake Terminal RailwayALU Alcolu RailroadALY Allegheny Railroad → Allegheny and Eastern RailroadAlabama and Mississippi RailroadAM Arkansas and Missouri RailroadAMC Amador Central RailroadAMHRAmherst Industries → Landisville RailroadAMIDAlabama Midland RailwayAMR Arcata and Mad River RailroadAMTAgence métropolitaine de transport (Montréal, Québec)AMTKAmtrak (National Railroad Passenger Corporation)AN Apalachicola Northern Railroad → AN RailwayANC Atlantic and North Carolina RailroadANE Abbotsford and Northeastern RailroadAnthony and Northern RailwayANR Angelina and Neches River RailroadANY Athabasca Northern RailwayAO Appalachian and Ohio RailroadAOK Arkansas-Oklahoma RailroadAOR Aliquippa and Ohio River RailroadAPA Apache RailwayAPD Albany Port DistrictAPNCAppanoose County Community RailroadAR Aberdeen and Rockfish RailroadARA Arcade and Attica RailroadARC Alexander RailroadARDPMissouri Pacific Railroad → Union Pacific RailroadARE A&R LineARMDArnaud RailwayARMHMissouri Pacific Railroad → Union Pacific RailroadARMNMissouri Pacific Railroad → Union Pacific RailroadARN Alberta RailNet → Canadian National RailwayARR Alaska RailroadARRGAltra RailroadARS Arkansas Southern RailroadARTAmerican Refrigerator Transit CompanyARW Arkansas Western RailwayARZCArizona and California RailroadAS Abilene and Southern Railway → Missouri Pacific RailroadAtlanta and St. Andrews Bay RailwayASABAtlanta and St. Andrews Bay Railway → Bay Line RailroadASDAAsbestos and Danville RailwayASMLAtlanta, Stone Mountain and Lithonia RailwayASR Allegheny Southern RailroadASRWAllegheny Southern RailwayASRYAshland RailwayATAuto TrainATCOArnold TransitATLTAT&L RailroadATNAlabama & Tennessee River RailwayATR Alliance Terminal RailroadATRWAnthracite RailwayATSFAtchison, Topeka and Santa Fe Railway → BNSF RailwayATW Atlantic and Western RailwayAUARAustin Area Terminal RailroadAUG Augusta RailroadAUNWAustin and Northwestern RailroadAUS Augusta Southern RailroadAUS Augusta and Summerville RailroadAUT Autauga Northern RailroadAlabama and Vicksburg RailwayAVNEAvera & Northeastern RailroadAVL Aroostook Valley RailroadAVR Allegheny Valley RailroadAVRR AG Valley RailroadAlexandria and Western RailwayAW Ahnapee and Western RailwayAWP Atlanta and West Point Railroad → Seaboard System Railroad → CSX TransportationAWRRAustin Western RailroadAWW Algers, Winslow and Western RailwayAYSSAllegheny and South Side RailwayAZERArizona Eastern RailwayAZS Arizona Southern Railroad
Others (assigned to companies or individuals who own railcars, but are not operating railroads)