Whyte notation

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A selection of early 20th century locomotive types according to their Whyte notation and their comparative size
Whyte notation from a handbook for railroad industry workers published in 1906[1]

The Whyte notation for classifying steam locomotives by wheel arrangement was devised by Frederick Methvan Whyte,[2] and came into use in the early twentieth century following a December 1900 editorial in American Engineer and Railroad Journal. The notation counts the number of leading wheels, then the number of driving wheels, and finally the number of trailing wheels, groups of numbers being separated by dashes.[3] Other classification schemes, like UIC classification and the French, Turkish and Swiss systems for steam locomotives, count axles rather than wheels.

In the notation a locomotive with two leading axles (four wheels) in front, then three driving axles (six wheels) and then one trailing axle (two wheels) is classified as 4-6-2.


Articulated locomotives[edit]

Articulated locomotives such as Garratts, which are effectively two locomotives joined by a common boiler, have a + between the arrangements of each engine. Thus a "double Pacific" type Garratt is a 4-6-2+2-6-4, for Garratt locomotives the + sign is used even when there are no intermediate unpowered wheels, e.g. the LMS Garratt 2-6-0+0-6-2. This is because the two engine units are more than just power bogies, they are complete engines, carrying fuel and water tanks. The + sign represents the bridge (carrying the boiler) that links the two engines.

Simpler articulated types such as Mallets, have a jointed frame under a common boiler where there are no unpowered wheels between the sets of powered wheels. Typically, the forward frame is free to swing, whereas the rear frame is rigid with the boiler, thus a Union Pacific Big Boy is a 4-8-8-4; four leading wheels, one group of eight driving wheels, another group of eight driving wheels, and then four trailing wheels.

Duplex locomotives[edit]

This numbering system is shared by duplex locomotives, which have powered wheel sets sharing a rigid frame.


No suffix means a tender locomotive.

T indicates a tank locomotive: in European practice, this is sometimes extended to indicate the type of tank locomotive: T means side tank, PT pannier tank, ST saddle tank, WT well tank. T+T means a tank locomotive that also has a tender.

In Europe, the suffix R can signify rack (0-6-0RT) or reversible (0-6-0TR), the latter being Bi-cabine locomotives used in France.

The suffix F indicates a fireless locomotive (0-4-0F), this locomotive has no tender.

Other suffixes have been used, including ng for narrow-gauge (less than 1,435 mm (4 ft 8 12 in) ) and CA or ca for compressed air (running on compressed air from a tank instead of steam from a boiler).

Internal combustion locomotives[edit]

In Britain, small diesel and petrol locomotives are usually classified in the same way as steam locomotives, e.g. 0-4-0, 0-6-0, 0-8-0. This may be followed by D for diesel or P for petrol, and another letter describing the transmission: E for electric, H hydraulic, M mechanical. Thus, 0-6-0DE denotes a six-wheel diesel locomotive with electric transmission. Where the axles are coupled by chains or shafts (rather than side rods) or are individually driven, the terms 4w, 6w or 8w are generally used. Thus, 4wPE indicates a four-wheel petrol locomotive with electric transmission, for large diesel locomotives the UIC classification is used.


The main limitation of Whyte Notation is that it does not cover non-standard types such as Shay locomotives, which use geared trucks rather than driving wheels, the most commonly used system in Europe outside the United Kingdom is UIC classification, based on German practice, which can define the exact layout of a locomotive.


In American (and to a lesser extent British) practice, most wheel arrangements in common use were given names, sometimes from the name of the first such locomotive built, for example, the 2-2-0 type arrangement is named Planet, after the 1830 locomotive on which it was first used. (This naming convention is similar to the naming of warship classes.)

Common wheel arrangements[edit]

The most common wheel arrangements are listed below; in the diagrams, the front of the locomotive is to the left.

(locomotive front is to the left)
Whyte classification Name # of units produced
Non-articulated locomotives
WheelArrangement 0-2-2.svg 0-2-2 Northumbrian
WheelArrangement 2-2-0.svg 2-2-0 Planet
WheelArrangement 2-2-2.svg 2-2-2 Single,[2] Jenny Lind
WheelArrangement 2-2-4.svg 2-2-4 Aerolite
WheelArrangement 4-2-0.svg 4-2-0 Jervis[4]
WheelArrangement 4-2-2.svg 4-2-2 Bicycle
WheelArrangement 4-2-4.svg 4-2-4 Huntington
WheelArrangement 6-2-0.svg 6-2-0 Crampton[5]
WheelArrangement 0-4-0.svg 0-4-0 Four-Coupled
WheelArrangement 0-4-4.svg 0-4-0+4 Four-Coupled as used on Railmotors
WheelArrangement 0-4-2.svg 0-4-2 Olomana
WheelArrangement 0-4-4.svg 0-4-4 Forney[1]
WheelArrangement 2-4-0.svg 2-4-0 Porter, 'Old English'[6]
WheelArrangement 2-4-2.svg 2-4-2 Columbia[1]
WheelArrangement 2-4-4.svg 2-4-4 Boston
WheelArrangement 4-4-0.svg 4-4-0 American,[1][7] Eight-wheeler
WheelArrangement 4-4-2.svg 4-4-2 Atlantic[1][8]
WheelArrangement 4-4-4.svg 4-4-4 Reading, Jubilee (Canada)[9]
WheelArrangement 0-6-0.svg 0-3-0 (one driving wheel per axle; used on Patiala State Monorail Trainways and also on the Listowel and Ballybunion Railway)
WheelArrangement 0-6-0.svg 0-6-0 Six-Coupled,[1] Bourbonnais (France), USRA 0-6-0 (United States)
WheelArrangement 0-6-2.svg 0-6-2 Branchliner, Webb
WheelArrangement 0-6-4.svg 0-6-4 Forney six-coupled[1]
WheelArrangement 0-6-6.svg 0-6-6
WheelArrangement 2-6-0.svg 2-6-0 Mogul[1][10] 11,000[11]
WheelArrangement 2-6-2.svg 2-6-2 Prairie[1][2]
WheelArrangement 2-6-4.svg 2-6-4 Adriatic
WheelArrangement 2-6-6.svg 2-6-6 Suburban
WheelArrangement 4-6-0.svg 4-6-0 Ten-Wheeler[1][12] (not Britain)[13]
WheelArrangement 4-6-2.svg 4-6-2 Pacific[1][2][14][15] 6,800[16]
WheelArrangement 4-6-4.svg 4-6-4 Hudson,[17] Baltic[2]
WheelArrangement 0-8-0.svg 0-8-0 Eight-Coupled,[1] USRA 0-8-0 (United States)
WheelArrangement 0-8-2.svg 0-8-2 Kado  [18]
WheelArrangement 0-8-4.svg 0-8-4 London
WheelArrangement 2-8-0.svg 2-8-0 Consolidation[1][2][19] 35,000[20]
WheelArrangement 2-8-2.svg 2-8-2 Mikado,[1][2] Mike, MacArthur[21][22]
WheelArrangement 2-8-4.svg 2-8-4 Berkshire, Kanawha[23][24]
WheelArrangement 2-8-6.svg 2-8-6 Used only on four Mason Bogie locomotives
WheelArrangement 4-8-0.svg 4-8-0 Twelve-Wheeler[1]
WheelArrangement 4-8-2.svg 4-8-2 Mountain,[2][25] Mohawk[26]
WheelArrangement 4-8-4.svg 4-8-4 Northern, Niagara, Confederation, Dixie, Greenbrier, Pocono, Potomac, Golden State (Southern Pacific),[27] Western, Laurentian (Delaware & Hudson Railroad), General, Wyoming (Lehigh Valley[28]), Governor, Big Apple, GS Series "Daylight" (Southern Pacific)[27]
WheelArrangement 4-8-6.svg 4-8-6 Proposed by Lima, never built
WheelArrangement 6-8-6.svg 6-8-6 (PRR S2 steam turbine locomotive)[29]
WheelArrangement 0-10-0.svg 0-10-0 Ten-Coupled,[1][30] (rarely) Decapod
WheelArrangement 0-10-2.svg 0-10-2 Union[30]
WheelArrangement 2-10-0.svg 2-10-0 Decapod,[1][31] Russian Decapod
WheelArrangement 2-10-2.svg 2-10-2 Santa Fe,[1] Central, Decapod (only on the Southern Pacific)
WheelArrangement 2-10-4.svg 2-10-4 Texas, Colorado (CB&Q), Selkirk (Canada)[32]
WheelArrangement 4-10-0.svg 4-10-0 Mastodon,[1] Gobernador (in honor of El Gobernador)
WheelArrangement 4-10-2.svg 4-10-2 Reid Tenwheeler,[33][34] Southern Pacific, Overland[35]
WheelArrangement 0-12-0.svg 0-12-0 Twelve-Coupled
WheelArrangement 2-12-0.svg 2-12-0 Centipede[1]
WheelArrangement 2-12-2.svg 2-12-2 Javanic
WheelArrangement 2-12-4.svg 2-12-4 Bulgaria
WheelArrangement 4-12-2.svg 4-12-2 Union Pacific[36]
WheelArrangement 4-14-4.svg 4-14-4 AA20[37]
Duplex locomotives
WheelArrangement 4-4-4-4.svg 4-4-4-4 (PRR T1)[38]
WheelArrangement 6-4-4-6.svg 6-4-4-6 (PRR S1)[39]
WheelArrangement 4-4-6-4.svg 4-4-6-4 (PRR Q2)[40]
WheelArrangement 4-6-4-4.svg 4-6-4-4 (PRR Q1)
Mallet[21] (simple and compound) articulated locomotives
WheelArrangement 0-4-4-0.svg 0-4-4-0 Bavarian BB II [41]
WheelArrangement 2-4-0.svgWheelArrangement 0-4-0.svg 2-4-4-0 Vivarais
WheelArrangement 0-4-0.svgWheelArrangement 0-4-2.svg 0-4-4-2 Swiss
WheelArrangement 2-4-4-2.svg 2-4-4-2 Skookum
4-4-6-2 AT&SF[42]
WheelArrangement 0-6-6-0.svg 0-6-6-0 Erie
WheelArrangement 2-6-6-0.svg 2-6-6-0 Denver & Salt Lake
WheelArrangement 2-6-6-2.svg 2-6-6-2 C&O/N&W. C&O Class H-2 thru H-5. Alco 1912.
WheelArrangement 2-6-6-4.svg 2-6-6-4 Norfolk & Western
WheelArrangement 2-6-6-6.svg 2-6-6-6 Allegheny,[43] Blue Ridge 68[44]
WheelArrangement 4-6-6-2.svg 4-6-6-2 (Southern Pacific class AM-2)[45]
WheelArrangement 4-6-6-4.svg 4-6-6-4 Challenger[46] 252[47]
WheelArrangement 2-6-8-0.svg 2-6-8-0 (Southern Railway, Great Northern Railway)[48]
WheelArrangement 0-8-8-0.svg 0-8-8-0 Angus
WheelArrangement 2-8-8-0.svg 2-8-8-0 Bull Moose
WheelArrangement 2-8-8-2.svg 2-8-8-2 Chesapeake, Norfolk & Western
WheelArrangement 2-8-8-4.svg 2-8-8-4 Yellowstone[49]
WheelArrangement 4-8-8-2.svg 4-8-8-2 Southern Pacific cab forward classes AC-4 through AC-12 (except AC-9)[45]
WheelArrangement 4-8-8-4.svg 4-8-8-4 Big Boy[50] 25[51]
WheelArrangement 2-10-10-2.svg 2-10-10-2 (Santa Fe and Virginian railroads)[48]
WheelArrangement 2-8-8-8-2.svg 2-8-8-8-2 Triplex (Erie RR)
WheelArrangement 2-8-8-8-4.svg 2-8-8-8-4 Triplex (Virginian RR)[52]
Garratt articulated locomotives
WheelArrangement 0-4-0+0-4-0.svg 0-4-0+0-4-0 Welsh Highland
WheelArrangement 0-6-6-0.svg 0-6-0+0-6-0 Kitson Meyer
WheelArrangement 2-4-4-2.svg 2-4-0+0-4-2 Double Porter
WheelArrangement 2-4-2+2-4-2.svg 2-4-2+2-4-2 Double Columbia
WheelArrangement 2-6-6-2.svg 2-6-0+0-6-2 Double Mogul
WheelArrangement 2-6-2+2-6-2.svg 2-6-2+2-6-2 Double Prairie
WheelArrangement 2-8-8-2.svg 2-8-0+0-8-2 Double Consolidation
WheelArrangement 2-8-2+2-8-2.svg 2-8-2+2-8-2 Double Mikado
WheelArrangement 4-4-2+2-4-4.svg 4-4-2+2-4-4 Double Atlantic
WheelArrangement 4-6-6-4.svg 4-6-0+0-6-4 Mogyana
WheelArrangement 4-6-2+2-6-4.svg 4-6-2+2-6-4 Double Pacific
WheelArrangement 4-6-4+4-6-4.svg 4-6-4+4-6-4 Double Baltic, Double Hudson
WheelArrangement 4-8-8-4.svg 4-8-0+0-8-4 Double Mastodon
WheelArrangement 4-8-2+2-8-4.svg 4-8-2+2-8-4 Double Mountain
WheelArrangement 4-8-4+4-8-4.svg 4-8-4+4-8-4 Double Northern

See also[edit]


  1. ^ a b c d e f g h i j k l m n o p q r s t Colvin, Fred H. (1906). The railroad pocket-book: a quick reference cyclopedia of railroad information. New York, Derry-Collard; London, Locomotive Publishing Company (US-UK co-edition). p. L‑9. 
  2. ^ a b c d e f g h "Steam Locomotive Glossary". Railway Technical Web Pages. 2007-06-28. Retrieved 2008-02-08. 
  3. ^ Thompson, Keith (2006-05-01). "Builder's plates: A locomotive's birth certificate". Kalmbach Publishing. Retrieved 2008-02-08. 
  4. ^ White, John H., Jr. (1968). A History of the American Locomotive - Its Development: 1830-1880. New York: Dover Publications. ISBN 0-486-23818-0.  , p. 33.
  5. ^ Adams, Bob (December 1968). "The Crampton Type Locomotive on the Camden & Amboy Railroad". NMRA Bulletin. National Model Railroad Association. 
  6. ^ Ellis, C Hamilton, Some Classic Locomotives, Allen & Unwin, 1949.173 p.
  7. ^ White (1968), p. 46.
  8. ^ Marsden, Richard (2008). "The LNER 4-4-2 Atlantic Locomotives". The London & North Eastern Railway (LNER) Encyclopedia. Retrieved 2008-02-08. 
  9. ^ "Canadian Pacific Railway No. 2929". Steamtown NHS Special History Study. United States National Park Service. 2002-02-14. Retrieved 2008-02-08. 
  10. ^ White (1968), p 62-65.
  11. ^ "Moguls, The 2-6-0". American-Rails.com. Retrieved 8 November 2016. 
  12. ^ White (1968), p. 57.
  13. ^ Marsden, Richard (2008). "LNER 4-6-0 Locomotives". The London & North Eastern Railway (LNER) Encyclopedia. Retrieved 2008-02-08. 
  14. ^ Marsden, Richard (2008). "LNER 4-6-2 Pacific Locomotives". The London & North Eastern Railway (LNER) Encyclopedia. Retrieved 2008-02-08. 
  15. ^ "Pacifics". SteamLocomotive.com. Retrieved 2008-02-08. 
  16. ^ "The 4-6-2 Pacific Type". American-Rails.com. Retrieved 8 November 2016. 
  17. ^ "Hudsons". SteamLocomotive.com. Retrieved 2008-02-08. 
  18. ^ Marsden, Richard (2008). "The Ivatt R1 0-8-2 Tank Locomotives". The London & North Eastern Railway (LNER) Encyclopedia. Archived from the original on 2007-09-27. Retrieved 2008-02-08. 
  19. ^ White (1968), p. 65.
  20. ^ "The 2-8-0 Consolidation Type". American-Rails.com. Retrieved 8 November 2016. 
  21. ^ a b "Glossary Of Common Railroad Terms: M". Kalmbach Publishing. Retrieved 2008-02-08. 
  22. ^ "The Mikado Type Locomotive". SteamLocomotive.com. Retrieved 2008-02-08. 
  23. ^ Farrell, Jack W. (1989). North American steam locomotives: The Berkshire and Texas types. Edmonds, WA: Pacific Fast Mail. ISBN 0-915713-15-2. 
  24. ^ "Berkshires & Kanawhas". SteamLocomotive.com. Retrieved 2008-02-08. 
  25. ^ "Mountains". SteamLocomotive.com. Retrieved 2008-02-08. 
  26. ^ Taylor, Frank (January 1941). "New York Central Dual-service Mohawk". Model Railroader. Kalmbach Publishing. 
  27. ^ a b "Northerns". SteamLocomotive.com. Retrieved 2008-02-08. 
  28. ^ http://www.steamlocomotive.com/northern/lv.shtml
  29. ^ Staufer, Alvin F.; Pennypacker, Bert (1962). Pennsy Power: Steam and Electric Locomotives of the Pennsylvania Railroad, 1900-1957. Research by Martin Flattley. Carollton, OH: Alvin F. Staufer. ISBN 978-0-9445-1304-0. LCCN 62020878. OCLC 602543182. 
  30. ^ a b Carlson, Neil (2006-07-03). "Steam locomotive profile: 0-10-0". Classic Trains. Kalmbach Publishing. Retrieved 2008-02-08. 
  31. ^ "Glossary Of Common Railroad Terms: D". Kalmbach Publishing. Retrieved 2008-02-08. 
  32. ^ "The Texas Type Locomotive". SteamLocomotive.com. Retrieved 2008-02-08. 
  33. ^ Paxton, Leith; Bourne, David (1985). Locomotives of the South African Railways (1st ed.). Cape Town: Struik. pp. 10–11, 31. ISBN 0869772112. 
  34. ^ Holland, D.F. (1971). Steam Locomotives of the South African Railways. 1: 1859–1910 (1st ed.). Newton Abbott, Devon: David & Charles. pp. 92–95, 123–124, 134–135. ISBN 978-0-7153-5382-0. 
  35. ^ Westing, Frederick (April 1954). "Baldwin's barnstorming behemoth". Trains. 
  36. ^ Westcott, Linn H. (1960). Model Railroader Cyclopedia - Volume 1: Steam Locomotives. Kalmbach Books. ISBN 0-89024-001-9. 
  37. ^ "Russian Reforms". 2001-10-06. Retrieved 2008-02-08. 
  38. ^ Russ, David (July 1943). "Riding the Pennsy T1". Trains. Kalmbach Publishing. 
  39. ^ Morgan, David P. (May 1965). "They called her the big engine". Trains. Kalmbach Publishing. 
  40. ^ Herring, S. E. & Morgan, David P. (June 1966). "Instead of a 4-10-4". Trains. Kalmbach Publishing. 
  41. ^ Barry, Frank (June 1963). "Mexico's inside-and-outside-framed 0-4-4-0s". Trains. Kalmbach Publishing. 
  42. ^ "The Jointed-Boiler Locomotives," Trains magazine, February 1945
  43. ^ "The Allegheny Type Locomotive". SteamLocomotive.com. Retrieved 2008-02-08. 
  44. ^ "The 2-6-6-6 Allegheny Type". American-Rails.com. Retrieved 8 November 2016. 
  45. ^ a b Diebert, Timothy S. & Strapac, Joseph A. (1987). Southern Pacific Company Steam Locomotive Conpendium. Shade Tree Books. ISBN 0-930742-12-5. 
  46. ^ "The Challenger Type Locomotive". SteamLocomotive.com. Retrieved 2008-02-08. 
  47. ^ "The 4-6-6-4 Challenger". American-Rails.com. Retrieved 8 November 2016. 
  48. ^ a b Carlson, Neil (2006-06-15). "Steam locomotive profile: 2-8-8-2". Classic Trains. Kalmbach Publishing. Retrieved 2008-02-08. 
  49. ^ "The Yellowstone Type Locomotive". SteamLocomotive.com. Retrieved 2008-02-08. 
  50. ^ "Union Pacific Big Boys". SteamLocomotive.com. Retrieved 2008-02-08. 
  51. ^ "Union Pacific Big Boy: The rebirth of a legend". Trains. 23 August 2013. Retrieved 8 November 2016. 
  52. ^ "Virginian Class XA Locomotives". SteamLocomotive.com. Retrieved 2008-02-08. 

Further reading[edit]

External links[edit]