A selection of early 20th century locomotive types according to their Whyte notation and their comparative size

Whyte notation as of 1906. 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 encouraged by an editorial in American Engineer and Railroad Journal (December 1900). Whyte's system 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.

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

[edit] Method

[edit] Articulated locomotives

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.

Simpler articulated types such as Mallets, where there are no unpowered axles between powered axles, have extra groups of numbers in the middle. Thus a Big Boy is a 4-8-8-4; there are two leading axles, one group of four driving axles, another group of four driving axles, and then two trailing axles.

[edit] Suffixes

The suffix T indicates a tank locomotive; otherwise, a tender locomotive is assumed. In British 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 has a tender for additional coal or water capacity.

In Europe, the suffix R could mean rack (0-6-0RT) or it could mean reversible (0-6-0TR). The latter case being the Bi-cabine locomotives used in France.

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

Other suffixes have been used at times, including ng for narrow-gauge locomotives (i.e., less than 56.5 in / 1435 mm) and CA or ca for compressed air (i.e., running on compressed air from a tank instead of steam).

[edit] Internal combustion locomotives

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, P 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.

[edit] Limitations

The limitations of the Whyte system in classifying locomotives that did not fit the standard steam locomotive pattern led to the design of other forms of classification. Most commonly used in Europe is the UIC classification scheme, based on German practice, which can more completely define the exact layout of a locomotive.

[edit] Naming

In American (and to a lesser extent British) practice, most wheel arrangements in common use were given names, often from the name of the first such locomotive built. (For example, the 2-2-0 is named Planet.) (This naming convention is reminiscent of the naming of warship classes.)

[edit] Common wheel arrangements

Here is a list of the most common wheel arrangements: in the illustration the front of the locomotive is to the left.

Arrangement (locomotive front is to the left)	Whyte classification	Name
Non-articulated locomotives
	0-2-2	Northumbrian
	2-2-0	Planet
	2-2-2	Single,[2] Jenny Lind
	2-2-4
	4-2-0	Jervis[4]
	4-2-2	Bicycle
	4-2-4
	6-2-0	Crampton[5]
	0-4-0	Four-Coupled
	0-4-2
	0-4-4	Forney[1]
	2-4-0	Porter, 'Old English'[6]
	2-4-2	Columbia[1]
	2-4-4
	4-4-0	American,[1][7] Eight-wheeler
	4-4-2	Atlantic[1][8]
	4-4-4	Reading, Jubilee (Canada)[9]
	0-3-0	(one driving wheel per axle; used on Patiala State monorail and also on the Listowel and Ballybunion Railway)
	0-6-0	Six-Coupled,[1] Bourbonnais (France), USRA 0-6-0 (United States)
	0-6-2
	0-6-4	Forney six-coupled[1]
	2-6-0	Mogul[1][10]
	2-6-2	Prairie[1][2]
	2-6-4	Adriatic
	2-6-6
	4-6-0	Ten-Wheeler[1][11] (not Britain)[12]
	4-6-2	Pacific[1][2][13][14]
	4-6-4	Hudson,[15] Baltic[2]
	0-8-0	Eight-Coupled,[1] USRA 0-8-0 (United States)
	0-8-2	[16]
	0-8-4
	2-8-0	Consolidation[1][2][17]
	2-8-2	Mikado,[1][2] Mike, MacArthur[18][19]
	2-8-4	Berkshire, Kanawha[20][21]
	2-8-6	Used only on four Mason Bogie locomotives
	4-8-0	Mastodon, Twelve-Wheeler[1]
	4-8-2	Mountain,[2][22] Mohawk[23]
	4-8-4	Northern, Niagara, Confederation, Dixie, Greenbrier, Pocono, Potomac, Golden State, Western, General, Governor, Big Apple, GS Series "Daylight" (Southern Pacific)[24]
	4-8-6	Proposed by Lima, never built
	6-8-6	(PRR S2 steam turbine locomotive)[25]
	0-10-0	Ten-Coupled,[1][26] (rarely) Decapod
	0-10-2	Union[26]
	2-10-0	Decapod,[1][27] Russian Decapod
	2-10-2	Santa Fe,[1] Central, Decapod (only on the Southern Pacific)
	2-10-4	Texas, Colorado (CB&Q), Selkirk (Canada)[28]
	4-10-0	Mastodon,[1] Gobernador (in honor of El Gobernador)
	4-10-2	Southern Pacific, Overland[29]
	0-12-0	Twelve-Coupled
	2-12-0	Centipede[1]
	2-12-2	Javanic
	2-12-4
	4-12-2	Union Pacific[30]
	4-14-4	AA20[31]
Duplex locomotives
	4-4-4-4	(PRR T1)[32]
	6-4-4-6	(PRR S1)[33]
	4-4-6-4	(PRR Q2)[34]
	4-6-4-4	(PRR Q1)
Mallet[18] (simple and compound) articulated locomotives
	0-4-4-0	Bavarian BB II [35]
	2-4-4-0
	0-4-4-2
	2-4-4-2
	0-6-6-0	Erie
	2-6-6-0	Denver & Salt Lake
	2-6-6-2
	2-6-6-4	Norfolk & Western
	2-6-6-6	Allegheny,[36] Blue Ridge
	4-6-6-2	(Southern Pacific class MM-2)[37]
	4-6-6-4	Challenger[38]
	2-6-8-0	(Southern Railway, Great Northern Railway)[39]
	0-8-8-0	Angus
	2-8-8-0	Bull Moose
	2-8-8-2	Chesapeake
	2-8-8-4	Yellowstone[40]
	4-8-8-2	Southern Pacific cab forward classes AC-4 through AC-12 (except AC-9)[37]
	4-8-8-4	Big Boy[41]
	2-10-10-2	(Santa Fe and Virginian railroads)[39]
	2-8-8-8-2	Triplex (Erie RR)
	2-8-8-8-4	Triplex (Virginian RR)[42]
Garratt articulated locomotives
	0-4-0+0-4-0
	2-6-2+2-6-2

[edit] References

• Boylan, Richard, and Barris, Wes (1991-05-30). "American Steam Locomotive Wheel Arrangements". SteamLocomotive.com. http://www.steamlocomotive.com/misc/wheels.shtml. Retrieved 2008-02-08. 
• White, John H., Jr. (1968). A History of the American Locomotive - Its Development: 1830-1880. New York: Dover Publications. ISBN 0-486-23818-0. 

[edit] See also

Wikimedia Commons has media related to: Whyte notation

• AAR wheel arrangement
• Wheel arrangement
• UIC classification
• Category:Locomotives by wheel arrangement