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A typical railbox boxcar.  Photo by Mike Chapman.

By Fourdee at English Wikipedia - Transferred from en.wikipedia to Commons by Oxyman using CommonsHelper., Public Domain, https://commons.wikimedia.org/w/index.php?curid=7005536

Classic Streamliners - TRAIN​CYCLOPEDIA

List of Reporting Marks - R

Note: Marks ending in U are for container owners; marks ending in X are not common carriers; marks ending in Z are for trailers without flanged wheels. All other marks are of common-carrier railroads.

RABU - Rabanco Companies
RACN - Raccoon River Railroad
RACU - Acciona Logistica
RACX - General Electric Rail Services Corporation
RACX - Union Tank Car Company (child mark of UTCX)
RAEU - Reach America Esg Ltd
RAFU - Oxitec S R L
RAFX - Rose Acre Farms Inc
RAGU - Rabanco Companies (child mark of RABU)
RAHU - IGL Limited
RAIL - Railinc Corporation (Switch Terminal Carrier)
RAIU - Rainbow Containers Gmbh
RAIX - Union Carbide Corporation (Subsidiary of Dow Chemical Company USA, child mark of UCFX)
RAJX - Rail Logix Alamo Junction, LLC (Elmendorf, TX)
RALU - Royal Arctic Line A/S
RALX - Radnor Rail Ltd
RAMX - Rail America
RAMX - Rail Merchants International
RANU - Rabanco Companies (child mark of RABU)
RAPX - Rapco Transportation Company
RARW - Rarus Railway Company (Class 3 Railroad)
RASU - Raseef Containers Services LLC
RASX - C A Rasmussen
RATU - Royal Atlantic LLC
RATX - Railtex Service Co Inc
RAVU - Flex Box Limited
RAWX - Platte River Power Authority
RAX - RPI-AAR Cooperative Test Program
RAX - Railroad Passenger Car Numbering Bureau (Shop Mark)
RBBN - Burlington Northern Railway
RBBQ - Burlington Northern Railway
RBBU - Besed
RBBX - Western Fruit Express; Ringling Brothers and Barnum and Bailey Circus
RBCS - Burlington Northern Railway
RBMN - Reading Blue Mountain and Northern Railroad; Reading and Northern
RBNX - Fruit Growers Express
RBOX - Railbox Company; TTX Corporation
RBW - Burlington Northern Railway

RC - Rosslyn Connecting Railroad
RCCX - Relco Nevada Corporation (Relco Tank Line Division)
RCOX - Arco Products Company
RCRX - Reagent Chemical and Research, Inc.
RCSX - Red-Corn Scrap Metals, Inc.
RDG - Reading Railroad; Norfolk Southern
RE - Relco
RECX - Central Louisiana Electric Company
REDX - Saudi Research and Development Corporation, Ltd. (REDEC)
REGX - Regus Industries LLC
RELX - Relco Nevada Corporation (Relco Tank Line Division)
RESX - Rescar, Inc.
RFCX - R&F Coal Company
RFMX - Robert F. Miller; Coldwell-Baker
RFP - Richmond, Fredericksburg and Potomac Railroad; CSX Transportation
RGCX - Rio Grande Chemical Sales Company
RGIX - Republic Gas and Utilities Corporation
RGS - Rio Grande Southern Railroad
RGW - Rio Grande Western Railway
RHAX - Sulphur Sales, Inc.
RHBX - R. H. Bogle Company
RHRX - Rahr Malting Company
RI - Chicago, Rock Island and Pacific Railroad (Rock Island)
RIIX - Reilly Industries, Inc.
RILX - Interail, Inc.
RJCC - R.J. Corman Railroad/Central Kentucky Lines
RJCP - R.J. Corman Railroad/Pennsylvania Lines
RJCW - R.J. Corman Railroad/Western Ohio Line
RJNX - R. H. Bogle Company
RKCX - Knox Kershaw, Inc.
RKGX - River King Coal Company
RKMW - Chicago, Rock Island and Pacific Railroad (Rock Island) Milwaukee Road directed operations
RLAX - Rail Logix, LLC (Ameriport/Baytown, TX)
RLGN - Mackenzie Northern Railway
RLCX - RELCO
RLGX - Rail Logix, LP (Port Crossing/La Porte, TX)
RLIX - Rail Link Inc.
RLK - Rail Link
RLKX - R. L. and S. S. Klein
RLSX - Robert L. Shipp
RMCX - Reynolds Metals Company
RMDX - American Refrigerator Transit Company
RMPX - Progress Rail Services Corporation; Railcar Ltd.
RMRX - Rocky Mountaineer
RNDX - ACF Industries
ROCK - Chicago, Rock Island and Pacific Railroad (Rock Island)
ROCX - Rock Island Improvement Company (Rock Island); Rocky Mountain Transportation Services
ROIX - Shintech, Inc.
ROYX - TCL, Inc.
RPCX - Railroad Passenger Car Numbering Bureau
RPRC - Richmond Pacific Railroad
RPRX - Railpower Hybrid Technologies Corp
RR - Conrail
RRC - Respondek Railroad Corporation
RREX - Rex Railway
RRLX - Railroad Resources, Inc. (maintenance of way cars)
RRLX - Rail Logistics Inc. / Rail Logistics LC
RRMX - Robertson's Ready Mix / RRM Properties Ltd, A California Limited Partnership
RRPX - Railroad Power Leasing
RRRR - Rock & Rail Inc.
RRRX - Rex Leasing, Inc.
RS - Roberval and Saguenay Railway
RSB - Rochester Subway
RSLX - RSL Corporation
RSOR - Riceboro Southern Railway
RSP - Roscoe, Snyder and Pacific Railway
RSPX - Evans Railcar Leasing
RSR - Rochester and Southern Railroad
RSS - Rochester Subway; Rockdale, Sandow and Southern Railroad
RSTX - RSTX, Inc.
RSUX - Riley Stoker Corporation
RSVX - RAILSERV Management Corporation
RSYX - Refined Sugars, Inc.
RT - River Terminals Railway
RTCX - Union Tank Car Company
RTDZ - Regional Transportation District; RTD Bus & Light Rail
RTEX - Rail Trusts Equipment
RTLX - Relco Nevada Corporation (Relco Tank Line Division)
RTMX - Richmond Leasing Company
RTPX - Wheelabrator Coal Services Company
RTTX - TTX Corporation
RUDX - Ruddy Tank Car Company
RUSX - US Rail Services, Inc.
RUT - Rutland Railroad; Vermont Railway
RV - Rahway Valley Railroad; Morristown & Erie
RVCX - Richter Vinegar Corporation
RVLX - Reinhardt Vinegar