This articlepossibly containsoriginal research. Pleaseimprove it byverifying the claims made and addinginline citations. Statements consisting only of original research should be removed.(September 2024) (Learn how and when to remove this message)

TheWhyte notation is a classification method forsteam locomotives, and some internal combustion locomotives andelectric locomotives, bywheel arrangement. It was devised byFrederick Methvan Whyte,^[2] and came into use in the early twentieth century following a December 1900 editorial inAmerican Engineer and Railroad Journal.

The notation was adopted and remains in use in North America and theUnited Kingdom to describe the wheel arrangements ofsteam locomotives, but for modernlocomotives,multiple units andtrams it has been supplanted by theUIC system in Europe and by theAAR 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.

The notation in its basic form counts the number ofleading wheels, then the number ofdriving wheels, and finally the number oftrailing 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 a4-6-2 locomotive, and is commonly known as aPacific.

Forarticulated locomotives that have two wheelsets, such asGarratts, which are effectively two locomotives joined by a commonboiler, each wheelset is denoted separately, with a plus sign (+) between them. Thus a 4-6-2-type Garratt is a4-6-2+2-6-4. For Garratt locomotives, the plus sign is used even when there are no intermediate unpowered wheels, e.g. theLMS Garratt2-6-0+0-6-2. This is because the two engine units are more than justpower 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 asMallets, 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, aUnion Pacific Big Boy is a4-8-8-4: 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 Belgianquadruplex locomotive, the arrangement is listed as 0-6-2+2-4-2-4-2+2-6-0.^[4]

Forduplex locomotives, which have two sets of coupled driving wheels mounted rigidly on the same frame, the same method is used as forMalletarticulated 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.

A number of standard suffixes can be used to extend the Whyte notation fortank locomotives:^[5]

Various other types of steam locomotive can be also denoted through suffixes:^[5]

The wheel arrangement of smalldiesel andpetrol 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, theUIC classification is more commonly used.

Various suffixes are also used to denote the different types of internal combustion locomotives:^[5]

The wheel arrangement of smallelectric locomotives can be denoted using this notation, like withinternal combustion locomotives.

Suffixes used for electric locomotives include:

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, the2-2-0 type arrangement is namedPlanet, afterthe 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.

Arrangement (locomotive front is to the left)	Whyte classification	Name	No. of units produced
Non-articulated locomotives
	0-2-2	Northumbrian (after the1830 locomotiveNorthumbrian)
	0-2-4
	2-2-0	Planet
	2-2-2	Single,[2] Jenny Lind[6]
	2-2-4	Aerolite
	4-2-0	Jervis[7]
	4-2-2	Bicycle[6]
	4-2-4	Huntington
	6-2-0	Crampton[8]
	0-4-0	Four-wheel switch[6]
	0-4-0+4
	0-4-2	Olomana
	0-4-4	Forney[1]
	2-4-0	Porter, 'Old English'[9]
	2-4-2	Columbia[1]
	2-4-4	Forney, Mason Bogie
	4-4-0	American,[1][10] eight-wheeler
	4-4-2	Atlantic[1][11]
	4-4-4	Reading, Jubilee (Canada)[12]
	0-3-0	(one driving wheel per axle; used onPatiala State Monorail Trainways and also on theListowel and Ballybunion Railway)
	0-6-0	Six-coupled,[1] Six-wheel switch,[6] Bourbonnais (France - tender), Boer (France - tank)
	0-6-2	Branchliner, Webb
	0-6-4	Forney six-coupled[1]
	0-6-6	Forney six-coupled
	2-6-0	Mogul[1][13]	11,000
	2-6-2	Prairie[1][2]
	2-6-4	Adriatic[6]
	2-6-6	Mason Bogie
	4-6-0	Ten-wheeler[1][14] (not Britain)[15]
	4-6-2	Pacific[1][2][16][17]	6,800
	4-6-4	Hudson,[18] Baltic[2]
	4-6-6	Use on theBoston and Albany Railroad.[19]
	0-8-0	Eight-coupled[1]
	0-8-2	Transfer
	0-8-4
	2-8-0	Consolidation[1][2][20]	35,000
	2-8-2	Mikado,[1][2] Mike, MacArthur[21][22]
	2-8-4	Berkshire, Kanawha[23][24]
	2-8-6	Used only on fourMason Bogie locomotives
	4-8-0	Twelve Wheeler,[1][25] Mastodon[6]
	4-8-2	Mountain,[2][26] Mohawk (NYC)[27]
	4-8-4	Northern, Niagara, Confederation, Dixie, Greenbrier, Pocono, Potomac, Heavy Mountain (Atchison, Topeka, and Santa Fe), Golden State (Southern Pacific),[28] Western, Laurentian (Delaware & Hudson Railroad), General, Wyoming (Lehigh Valley[29]), Governor,Big Apple,GS Series "Daylight" (Southern Pacific)[28]
	4-8-6	Proposed byLima, never built
	6-8-6	Turbine, only used on the PRR S2 Steam Turbine	1
	0-10-0	Ten-coupled,[1][30] Ten-wheel switch[6]
	0-10-2	Union[30]
	2-10-0	Decapod,[1][31]Russian Decapod
	2-10-2	Santa Fe[1]
	2-10-4	Texas, Colorado (CB&Q), Selkirk (Canada)[32]
	2-10-6	Proposed byIndian Railways, never built[33]
	4-10-0	Mastodon[1][25]
	4-10-2	Reid Tenwheeler,[34][35]Southern Pacific, Overland,[36] Super Mountain[6]
	0-12-0	12-coupled
	0-12-2	Used in Argentina
	2-12-0	Centipede[1]
	2-12-2	Javanic[6]	30
	2-12-4		20
	2-12-6	Proposed byLima, never built
	4-12-2	Union Pacific[37]
	4-14-4	AA20,[38] Soviet[6]	1
Divided drive and duplex locomotives
	0-2-2-0	Used on theMount Washington Cog Railway
	2-2-2-0
	2-2-2-2
	2-2-4-0		1
	4-2-2-0	Double single[39]
	2-4-6-2
	4-4-4-2	Planned for proposedACE 3000 locomotive.
	4-4-4-4	(PRR T1)[40]	53
	6-4-4-6	(PRR S1)[41]	1
	4-4-6-4	(PRR Q2)[42]	26
	4-6-4-4	(PRR Q1)	1
Articulated locomotives (simple and compound)
	0-4-4-0
	2-4-4-0		5
	0-4-4-2
	2-4-4-2	Little River
	4-4-6-2	Used by the Santa Fe[43]	2
	0-6-6-0
	2-6-6-0
	2-6-6-2		1,300
	2-6-6-4		60
	2-6-6-6	Allegheny,[44] Blue Ridge	68
	4-6-6-2	(Southern Pacific class AM-2)[45]
	4-6-6-4	Challenger[46]	252
	0-8-6-0
	2-6-8-0	(Southern Railway, Great Northern Railway)[47]	39
	0-8-8-0	Angus[48]
	2-8-8-0	Bull Moose
	2-8-8-2	Chesapeake	222
	2-8-8-4	Yellowstone[49]	78
	4-8-8-2	Cab Forward	195
	4-8-8-4	Big Boy[50]	25[51]
	2-10-10-2	(Santa Fe and Virginian railroads)[47]	20
	2-8-8-8-2	Triplex (Erie RR)	3
	2-8-8-8-4	Triplex (Virginian RR)[52]	1
Garratt articulated locomotives
	0-4-0+0-4-0
	0-6-0+0-6-0
	2-4-0+0-4-2
	2-4-2+2-4-2
	2-6-0+0-6-2
	2-6-2+2-6-2	Double Prairie
	2-8-0+0-8-2
	2-8-2+2-8-2	Double Mikado
	4-4-2+2-4-4
	4-6-0+0-6-4
	4-6-2+2-6-4	Double Pacific
	4-6-4+4-6-4	Double Hudson
	4-8-0+0-8-4
	4-8-2+2-8-4
	4-8-4+4-8-4

• AAR wheel arrangement
• Swiss locomotive and railcar classification
• UIC classification
• Wheel arrangement

• Boylan, Richard; Barris, Wes (30 May 1991)."American Steam Locomotive Wheel Arrangements".SteamLocomotive.com. Archived fromthe original on 26 January 2008. Retrieved8 February 2008.

• Media related toWhyte notation at Wikimedia Commons

In the various names above of a 4-8-4, omitted was the letters "F E F" which simply means: four eight four.

• Whyte notation
• 1900s introductions
• Locomotive classification systems
• Locomotives by wheel arrangement
• Notation

• CS1 errors: periodical ignored
• CS1 maint: location missing publisher
• CS1: long volume value
• Articles with short description
• Short description is different from Wikidata
• Use dmy dates from August 2021
• Articles that may contain original research from September 2024
• All articles that may contain original research
• Commons category link is on Wikidata