Locomotive model abbreviations

Deciphering an alphabet soup
RELATED TOPICS: LOCOMOTIVES | SUPPLIERS
Letters in locomotive models do indeed stand for something.

Often the words they represent describe some feature of the locomotive, like wheel arrangement or type of propulsion equipment. Sometimes the letters stand for the type of service the locomotive is intended for. A few are just catchy marketing terms, like Century or Consolidation.

Here's a list of the letters found in the more common model series, grouped by builder:

ELECTRO-MOTIVE DIVISION
SC Six-hundred h.p., Cast frame
SW Six-hundred h.p., Welded frame
NC Nine-hundred h.p., Cast frame
NW Nine-hundred h.p., Welded frame
E Eighteen-hundred h.p.
F Fourteen-hundred h.p.
TR Transfer
BL Branch Line
GP General Purpose
SD Special Duty
F Full-width carbody (as in F40)
DD D-D wheel arrangement
MP Multi-Purpose
M Wide nose and safety cab
I Partially isolated "whisper cab"
MAC Wide nose and safety cab or whisper cab, plus an alternating-current (A.C.) drive system
ACe A.C. drive system meeting EPA Tier 2 emissions requirements

GENERAL ELECTRIC
U Universal
B B-B wheel arrangement
C C-C wheel arrangement
P Passenger
AC Alternating Current
DC Direct Current
W Wide nose and safety cab
ES Evolution Series

ALCO/MLW
HH High Hood
DL Diesel Locomotive
S Switcher
T Transfer
FA Freight, A-unit (FB indicates Freight, B-unit)
PA Passenger, A-unit
RS Road-Switcher
C Century
M Montreal Locomotive Works

BALDWIN
VO Model VO engine
DS Diesel Switcher
S Switcher
DRS Diesel Road-Switcher
RS Road-Switcher
AS All-Service
DR Diesel Road
RF Road Freight

FAIRBANKS-MORSE
H Hood carbody
CFA Consolidation Line (C-Line), Freight, A-unit
CPA C-Line, Passenger, A-unit

Model designations sometimes persist after the series has evolved beyond the letters' original meaning. Long after EMD's welded-frame yard engines surpassed their original 600 h.p. rating, the line was still tagged SW, with the letters coming to be understood to mean switcher. Descendants of the first E's and Fs hit 2400 and 1750 h.p., respectively, but EMD retained their letter series for the sake of continuity.
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