A selection of early 20th century locomotive types according to their Whyte notation and their comparative sizeWhyte notation from a handbook for railroad industry workers published in 1906[1]
The Whyte notation is a classification method for steam locomotives, and some internal combustion locomotives and electric locomotives, by wheel arrangement. It 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 was adopted and remains in use in North America and the United Kingdom to describe the wheel arrangements of steam locomotives, but for modern locomotives, multiple units and trams it has been supplanted by the UIC system in Europe and by the AAR system (essentially a simplification of the UIC system) in North America. However, geared steam locomotives do not use the notation. They are classified by their model and their number of trucks.
Structure of the system
Basic form
The notation in its basic form counts the number of leading wheels, then the number of driving wheels, and finally the number of trailing wheels, numbers being separated by dashes.[3] For example, 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 a 4-6-2 locomotive, and is commonly known as a Pacific.
Denotion of other locomotives
Articulated locomotives
For articulated locomotives that have two wheelsets, such as Garratts, which are effectively two locomotives joined by a common boiler, each wheelset is denoted separately, with a plus sign (+) between them. Thus a 4-6-2-type Garratt is a 4-6-2+2-6-4. For Garratt locomotives, the plus sign is used even when there are no intermediate unpowered wheels, e.g. the LMS Garratt2-6-0+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 plus 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. Sometimes articulated locomotives of this type are denoted with a “+” between each driving wheels set (so in the previous case, the Big Boy would be a 4-8+8-4). This may have been developed to distinguish articulated and duplex arrangements; duplex arrangements would get a “-“ being rigid and articulated locomotives would get a “+” being flexible. However, given all the wheel arrangements for duplex locomotives have been mutually exclusive to them, it is usually considered unnecessary and thus another “-“ is usually used.
Triplex locomotives, and any theoretical larger ones, simply expand on basic articulated locomotives, for example, 2-8-8-8-2. In the case of the Belgian quadruplex locomotive, the arrangement is listed as 0-6-2+2-4-2-4-2+2-6-0.[4]
Duplex locomotives
For duplex locomotives, which have two sets of coupled driving wheels mounted rigidly on the same frame, the same method is used as for Malletarticulated locomotives – the number of leading wheels is placed first, followed by the leading set of driving wheels, followed by the trailing set of driving wheels, followed by the trailing wheels, each number being separated by a hyphen.
Tank locomotives
A number of standard suffixes can be used to extend the Whyte notation for tank locomotives:[5]
The wheel arrangement of small diesel and petrol locomotives can be classified using the same notation as steam locomotives, e.g. 0-4-0, 0-6-0, 0-8-0. Where the axles are coupled by chains or shafts (rather than side rods) or are individually driven, the terms 4w (4-wheeled), 6w (6-wheeled) or 8w (8-wheeled) are generally used. For larger locomotives, the UIC classification is more commonly used.
Various suffixes are also used to denote the different types of internal combustion locomotives:[5]
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.) Note that several wheel arrangements had multiple names, and some names were only used in some countries.
Wheel arrangements under the Whyte system are listed below. In the diagrams, the front of the locomotive is to the left.
^ abcdefghijDirectory of Railway Officials & Year Book 1956-1957. London: Tothill Press Limited. 1956. p. 421.
^White, John H. Jr. (1968). A History of the American Locomotive - Its Development: 1830-1880. New York: Dover Publications. ISBN0-486-23818-0., p. 33.
^Adams, Bob (December 1968). "The Crampton Type Locomotive on the Camden & Amboy Railroad". NMRA Bulletin. National Model Railroad Association.
^Ellis, C Hamilton, Some Classic Locomotives, Allen & Unwin, 1949.173 p.
^Marsden, Richard (2008). "The LNER 4-4-2 Atlantic Locomotives". The London & North Eastern Railway (LNER) Encyclopedia. Archived from the original on 13 February 2008. Retrieved 8 February 2008.
^"Canadian Pacific Railway No. 2929". Steamtown NHS Special History Study. United States National Park Service. 14 February 2002. Archived from the original on 19 May 2007. Retrieved 8 February 2008.
^Marsden, Richard (2008). "LNER 4-6-0 Locomotives". The London & North Eastern Railway (LNER) Encyclopedia. Archived from the original on 13 February 2008. Retrieved 8 February 2008.
^Marsden, Richard (2008). "LNER 4-6-2 Pacific Locomotives". The London & North Eastern Railway (LNER) Encyclopedia. Archived from the original on 25 February 2008. Retrieved 8 February 2008.
^"Pacifics". SteamLocomotive.com. Archived from the original on 25 January 2008. Retrieved 8 February 2008.
^"Hudsons". SteamLocomotive.com. Archived from the original on 27 January 2008. Retrieved 8 February 2008.
^Farrell, Jack W. (1989). North American steam locomotives: The Berkshire and Texas types. Edmonds, WA. ISBN0-915713-15-2. {{cite book}}: |work= ignored (help)CS1 maint: location missing publisher (link)
^ abCarlson, Neil (3 July 2006). "Steam locomotive profile: 0-10-0". Classic Trains. Kalmbach Publishing. Archived from the original on 29 September 2007. Retrieved 8 February 2008.
^Paxton, Leith; Bourne, David (1985). Locomotives of the South African Railways (1st ed.). Cape Town: Struik. pp. 10–11, 31. ISBN0869772112.
^Holland, D.F. (1971). Steam Locomotives of the South African Railways. Vol. 1: 1859–1910 (1st ed.). Newton Abbott, England: David & Charles. pp. 92–95, 123–124, 134–135. ISBN978-0-7153-5382-0.
^Westing, Frederick (April 1954). "Baldwin's barnstorming behemoth". Trains.
^Westcott, Linn H. (1960). Model Railroader Cyclopedia - Volume 1: Steam Locomotives. Kalmbach Books. ISBN0-89024-001-9.
^"Russian Reforms". 6 October 2001. Archived from the original on 18 October 2010. Retrieved 8 February 2008.
^ abCarlson, Neil (15 June 2006). "Steam locomotive profile: 2-8-8-2". Classic Trains. Kalmbach Publishing. Archived from the original on 16 November 2008. Retrieved 8 February 2008.
