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, and came into use in the early twentieth century following a December 1900 editorial in American Engineer and Railroad Journal.
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. 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
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 "double Pacific" 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 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 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.
For duplex locomotives, which have two sets of coupled driving wheels mounted rigidly on the same frame, the same method is used as for Mallet articulated locomotives – the amount of leading wheels are 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.
|[No Suffix]||Tender locomotive||0-6-0|
|T||Side tank locomotive||0-6-2T|
|ST||Saddle tank locomotive||0-4-0ST|
|WT||Well tank locomotive||0-4-0WT|
|PT||Pannier tank locomotive||0-6-0PT|
|C or CT||Crane tank locomotive||0-6-2CT|
|IST||Inverted saddle tank locomotive||0-4-2IST|
|T+T (or ST+T, WT+T, etc.)||Tank locomotive which also has a tender||4-6-2T+T|
Other steam locomotives
Various other types of steam locomotive can be also denoted through suffixes:
|VB or VBT||Vertical boilered locomotive||0-6-0VB|
|CA||Compressed air locomotive||0-6-0CA|
|R or RT||Rack locomotive||0-4-0RT|
Internal combustion locomotives
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:
Suffixes used for Electric locomotives include:
|OE||Overhead-lines electric locomotive||0-8-0OE|
Wheel arrangement names
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
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||No. of units produced|
|2-2-2||Patentee, Single, Jenny Lind|
|4-2-2||Bicycle, Iron Duke, Single|
|0-4-0+4||Four-coupled as used on railmotors|
|2-4-0||Porter, 'Old English'|
|4-4-4||Reading, Jubilee (Canada)|
|0-3-0||(one driving wheel per axle; used on Patiala State Monorail Trainways and also on the Listowel and Ballybunion Railway)|
|0-6-0||Six-coupled, Bourbonnais (France), USRA 0-6-0 (United States)|
|4-6-0||Ten-wheeler (not Britain)|
|4-6-6||Use on the Boston and Albany Railroad.|
|0-8-0||Eight-coupled, USRA 0-8-0 (United States)|
|2-8-2||Mikado, Mike, MacArthur|
|2-8-6||Used only on four Mason Bogie locomotives|
|4-8-0||Twelve Wheeler |
|4-8-2||Mountain, Mohawk (NYC)|
|4-8-4||Northern, Niagara, Confederation, Dixie, Greenbrier, Pocono, Potomac, Golden State (Southern Pacific), Western, Laurentian (Delaware & Hudson Railroad), General, Wyoming (Lehigh Valley), Governor, Big Apple, GS Series "Daylight" (Southern Pacific)|
|4-8-6||Proposed by Lima, never built|
|6-8-6||(PRR S2 steam turbine locomotive)||1|
|0-10-0||Ten-coupled, (rarely) Decapod|
|2-10-0||Decapod, Russian Decapod|
|2-10-2||Santa Fe, Central, Decapod (only on the Southern Pacific)|
|2-10-4||Texas, Colorado (CB&Q), Selkirk (Canada)|
|4-10-2||Reid Tenwheeler, Southern Pacific, Overland|
|2-12-6||Proposed by Lima, never built|
|Articulated locomotives (simple and compound)|
|0-4-4-0||Bavarian BB II |
|2-6-6-0||Denver & Salt Lake|
|2-6-6-2||C&O/N&W. C&O Class H-2 thru H-5. Alco 1912.||1,300|
|2-6-6-4||Norfolk & Western||60|
|2-6-6-6||Allegheny, Blue Ridge||68|
|4-6-6-2||(Southern Pacific class AM-2)|
|2-6-8-0||(Southern Railway, Great Northern Railway)||39|
|2-8-8-2||Chesapeake, Norfolk & Western||222|
|4-8-8-2||Southern Pacific cab forward classes AC-4 through AC-12 (except AC-9)||195|
|2-10-10-2||(Santa Fe and Virginian railroads)||20|
|2-8-8-8-2||Triplex (Erie RR)||3|
|2-8-8-8-4||Triplex (Virginian RR)||1|
|Garratt articulated locomotives|
|4-6-4+4-6-4||Double Baltic, Double Hudson|
- AAR wheel arrangement
- Swiss locomotive and railcar classification
- UIC classification
- Wheel arrangement
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In the various names above of a 4-8-4, omitted was the letters "F E F" which simply means: four eight four.