# Whyte notation

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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.

## Method

### 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 locomotive, and is commonly known as a Pacific.

### 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 "double Pacific" type Garratt is a . For Garratt locomotives, the plus sign is used even when there are no intermediate unpowered wheels, e.g. the LMS Garratt . 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 ; four leading wheels, one group of eight driving wheels, another group of eight driving wheels, and then four trailing wheels.

### 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 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.

### Tank locomotives

A number of standard suffixes can be used to extend the Whyte notation for tank locomotives: [4]

SuffixMeaningExample
[No Suffix] Tender locomotive
T Side tank locomotive
WT Well tank locomotive
PT Pannier tank locomotive
C or CT Crane tank locomotive
T+T (or ST+T, WT+T, etc.) Tank locomotive which also has a tender

### Other steam locomotives

Various other types of steam locomotive can be also denoted through suffixes: [4]

 VB or VBT Vertical boilered locomotive F Fireless locomotive CA Compressed air locomotive R Railcar R or RT Rack locomotive G Geared locomotive

### 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: [4]

SuffixMeaningExample
PM Petrol-mechanical locomotive
PE Petrol-electric locomotive
D Diesel locomotive
DM Diesel–mechanical locomotive
DE Diesel–electric locomotive
DH Diesel–hydraulic locomotive

### Electric locomotives

The wheel arrangement of small electric locomotives can be denoted using this notation, like with internal combustion locomotives.

Suffixes used for Electric locomotives include:

SuffixMeaningExample
BE Battery-electric locomotive

## 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.

Arrangement
(locomotive front is to the left)
Whyte classificationNameNo. of units produced
Non-articulated locomotives
0-2-2 Northumbrian
2-2-0 Planet
2-2-2 Patentee, Single, [2] Jenny Lind
2-2-4 Aerolite
4-2-0 Jervis [5]
4-2-2 Bicycle, Iron Duke, Single
4-2-4 Huntington
6-2-0 Crampton [6]
0-4-0 Four-coupled
0-4-0+4 Four-coupled as used on railmotors
0-4-2 Olomana
0-4-4 Forney [1]
2-4-0 Porter, 'Old English' [7]
2-4-2 Columbia [1]
2-4-4 Boston
4-4-0 American, [1] [8] eight-wheeler
4-4-2 Atlantic [1] [9]
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, [1] Bourbonnais (France), USRA 0-6-0 (United States)
0-6-2 Branchliner, Webb
0-6-4 Forney six-coupled [1]
0-6-6
2-6-0 Mogul [1] [11] 11,000
2-6-2 Prairie [1] [2]
2-6-6 Suburban
4-6-0 Ten-wheeler [1] [12] (not Britain) [13]
4-6-2 Pacific [1] [2] [14] [15] 6,800
4-6-4 Hudson, [16] Baltic [2]
0-8-0 Eight-coupled, [1] USRA 0-8-0 (United States)
0-8-2
0-8-4 London
2-8-0 Consolidation [1] [2] [17] 35,000
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 [1]
4-8-2 Mountain, [2] [22] Mohawk (NYC) [23]
4-8-4 Northern, Niagara, Confederation, Dixie, Greenbrier, Pocono, Potomac, Golden State (Southern Pacific), [24] Western, Laurentian (Delaware & Hudson Railroad), General, Wyoming (Lehigh Valley [25] ), 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) [26] 1
0-10-0 Ten-coupled, [1] [27] (rarely) Decapod
0-10-2 Union [27]
2-10-0 Decapod, [1] [28] Russian Decapod
2-10-2 Santa Fe, [1] Central, Decapod (only on the Southern Pacific)
4-10-2 Reid Tenwheeler, [30] [31] Southern Pacific, Overland [32]
0-12-0 Twelve-coupled
2-12-0 Centipede [1]
2-12-2 Javanic
2-12-4 Bulgaria
2-12-6 Proposed by Lima, never built
4-12-2 Union Pacific [33] 88
4-14-4 AA20 [34] 1
Duplex locomotives
4-4-4-4 (PRR T1) [35]
6-4-4-6 (PRR S1) [36] 1
4-4-6-4 (PRR Q2) [37] 26
4-6-4-4 (PRR Q1)1
Articulated locomotives (simple and compound)
0-4-4-0 Bavarian BB II [38]
2-4-4-0 Vivarais
0-4-4-2 Swiss
2-4-4-2
4-4-6-2 AT&SF [39] 2
0-6-6-0 Erie
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.
2-6-6-4 Norfolk & Western60
2-6-6-6 Allegheny, [40] Blue Ridge68
4-6-6-2 (Southern Pacific class AM-2) [41]
4-6-6-4 Challenger [42] 252
2-6-8-0 (Southern Railway, Great Northern Railway) [43]
0-8-8-0 Angus
2-8-8-0 Bull Moose
2-8-8-2 Chesapeake, Norfolk & Western
2-8-8-4 Yellowstone [44] 78
4-8-8-2 Southern Pacific cab forward classes AC-4 through AC-12 (except AC-9) [41] 195
4-8-8-4 Big Boy [45] 25 [46]
2-10-10-2 (Santa Fe and Virginian railroads) [43] 20
2-8-8-8-2 Triplex (Erie RR)3
2-8-8-8-4 Triplex (Virginian RR) [47] 1
Garratt articulated locomotives
0-4-0+0-4-0 Welsh Highland
0-6-0+0-6-0 Kitson Meyer
2-4-0+0-4-2 Double Porter
2-4-2+2-4-2 Double Columbia
2-6-0+0-6-2 Double Mogul
2-6-2+2-6-2 Double Prairie
2-8-0+0-8-2 Double Consolidation
4-4-2+2-4-4 Double Atlantic
4-6-0+0-6-4 Mogyana
4-6-2+2-6-4 Double Pacific
4-6-4+4-6-4 Double Baltic, Double Hudson
4-8-0+0-8-4 Double Mastodon
4-8-2+2-8-4 Double Mountain
4-8-4+4-8-4 Double Northern

## Related Research Articles

A steam locomotive is a type of railway locomotive that produces its pulling power through a steam engine. These locomotives are fuelled by burning combustible material—usually coal, wood, or oil—to produce steam in a boiler. The steam moves reciprocating pistons which are mechanically connected to the locomotive's main wheels (drivers). Both fuel and water supplies are carried with the locomotive, either on the locomotive itself or in wagons (tenders) pulled behind.

Under the Whyte notation for the classification of steam locomotives, a 2-10-4 locomotive has two leading wheels on one axle, usually in a bissel truck, ten coupled driving wheels on five axles, and four trailing wheels on two axles, usually in a bogie. These were referred to as the Texas type in most of the United States, the Colorado type on the Burlington Route and the Selkirk type in Canada.

Under the Whyte notation for the classification of steam locomotives, 2-10-0 represents the wheel arrangement of two leading wheels on one axle, ten powered and coupled driving wheels on five axles, and no trailing wheels. This arrangement was often named Decapod, especially in the United States, although this name was sometimes applied to locomotives of 0-10-0 "Ten-Coupled" arrangement, particularly in the United Kingdom. Notable German locomotives of this type include the war locomotives of Class 52.

The UIC classification of locomotive axle arrangements, sometimes known as German classification or German system, describes the wheel arrangement of locomotives, multiple units and trams. It is set out in the International Union of Railways (UIC) "Leaflet 650 – Standard designation of axle arrangement on locomotives and multiple-unit sets". It is used in much of the world. The United Kingdom uses the Whyte notation. The United States uses the simplified AAR wheel arrangement for modern locomotives.

Rail terminology is a form of technical terminology. The difference between the American term railroad and the international term railway is the most significant difference in rail terminology. There are also others, due to the parallel development of rail transport systems in different parts of the world.

Under the Whyte notation for the classification of steam locomotives by wheel arrangement, 4-4-2 represents a configuration of four leading wheels on two axles, usually in a leading bogie with a single pivot point, four powered and coupled driving wheels on two axles, and two trailing wheels on one axle, usually in a trailing truck which supports part of the weight of the boiler and firebox and gives the class its main improvement over the 4-4-0 configuration.

Under the Whyte notation for the classification of steam locomotives, 0-8-0 represents the wheel arrangement of no leading wheels, eight powered and coupled driving wheels on four axles and no trailing wheels. Locomotives of this type are also referred to as eight coupled.

Under the Whyte notation for the classification of steam locomotives, 4-12-2 represents the wheel arrangement of four leading wheels, twelve coupled driving wheels, and two trailing wheels. This arrangement was named the Union Pacific type, after the only railroad to use it, the Union Pacific Railroad.

Under the Whyte notation for the classification of steam locomotives by wheel arrangement, 2-6-6-0 is a locomotive with one pair of unpowered leading wheels, followed by two sets of three pairs of powered driving wheels and no trailing wheels. The wheel arrangement was principally used on Mallet-type articulated locomotives. Some tank locomotive examples were also built, for which various suffixes to indicate the type of tank would be added to the wheel arrangement, for example 2-6-6-0T for an engine with side-tanks.

The term cab forward refers to various rail and road vehicle designs that place the driver's compartment substantially farther towards the front than is common practice.

Under the Whyte notation for the classification of steam locomotives by wheel arrangement, the 2-8-0+0-8-2 is a Garratt articulated locomotive. The wheel arrangement is effectively two 2-8-0 locomotives operating back to back, with the boiler and cab suspended between the two power units. Each power unit has a single pair of leading wheels in a leading truck, followed by four coupled pairs of driving wheels and no trailing wheels. Since the 2-8-0 type is sometimes known as a Consolidation, the corresponding Garratt type could be referred to as a Double Consolidation.

Under the Whyte notation for the classification of steam locomotives by wheel arrangement, a 4-6-2+2-6-4 is a Garratt or Union Garratt articulated locomotive using a pair of 4-6-2 engine units back to back, with the boiler and cab suspended between them. The 4-6-2 wheel arrangement of each engine unit has four leading wheels on two axles, usually in a leading bogie, six powered and coupled driving wheels on three axles, and two trailing wheels on one axle, usually in a trailing truck. Since the 4-6-2 type is known as a Pacific, the corresponding Garratt type is usually known as a Double Pacific.

Under the Whyte notation for the classification of steam locomotives, 2-6-0+0-6-2 represents the wheel arrangement of an articulated locomotive with two separate swivelling engine units, arranged back to back with the boiler and cab suspended between them. Each engine unit has two leading wheels in a leading truck, six powered and coupled driving wheels on three axles and no trailing wheels.

Under the Whyte notation for the classification of steam locomotives by wheel arrangement, the 0-4-0+0-4-0 is an articulated locomotive of the Garratt type. The wheel arrangement is effectively two 0-4-0 locomotives operating back-to-back or face-to-face, with the boiler and cab suspended between the two power units. Each power unit has no leading wheels, four powered and coupled driving wheels on two axles and no trailing wheels. A similar arrangement exists for Mallet and Meyer locomotives, but is referred to as 0-4-4-0.

Under the Whyte notation for the classification of steam locomotives by wheel arrangement, the 4-8-4+4-8-4 is a Garratt articulated locomotive. The wheel arrangement is effectively two 4-8-4 locomotives operating back to back, with the boiler and cab suspended between the two engine units. Each engine unit has two pairs of leading wheels in a leading bogie, followed by four coupled pairs of driving wheels and two pairs of trailing wheels in a trailing bogie. Since the 4-8-4 type is sometimes known as a Northern, the corresponding Garratt type would be referred to as a Double Northern.

Under the Whyte notation for the classification of steam locomotives, 0-6-0+0-6-0 represents the wheel arrangement of an articulated locomotive with two separate swivelling engine units, each unit with no leading wheels, six powered and coupled driving wheels on three axles and no trailing wheels. The arrangement is effectively two 0-6-0 locomotives operating back-to-back and was used on Garratt, Double Fairlie, Meyer and Kitson-Meyer articulated locomotives. A similar arrangement exists for Mallet steam locomotives on which only the front engine unit swivels, but these are referred to as 0-6-6-0.

Under the Whyte notation for the classification of steam locomotives by wheel arrangement, 2-4-0+0-4-2 is an articulated locomotive, usually of the Garratt type. The wheel arrangement is effectively two 2-4-0 locomotives operating back to back, with the boiler and cab suspended between the two power units. Each power unit has two leading wheels on one axle, four powered and coupled driving wheels on two axles and no trailing wheels. Since the 2-4-0 type is sometimes known as a Porter, the corresponding Garratt type would be referred to as a Double Porter. A similar wheel arrangement exists for Mallet locomotives, but is referred to as 2-4-4-2.

Under the Whyte notation for the classification of steam locomotives by wheel arrangement, the 2-4-2+2-4-2 is a Garratt articulated locomotive. The wheel arrangement is effectively two 2-4-2 locomotives operating back to back, with the boiler and cab suspended between the two power units. Each power unit has a single pair of leading wheels in a leading truck, followed by two coupled pairs of driving wheels, with a single pair of trailing wheels in a trailing truck. Since the 2-4-2 type is sometimes known as a Columbia, the corresponding Garratt type could be referred to as a Double Columbia.

Under the Whyte notation for the classification of steam locomotives by wheel arrangement, the 4-8-0+0-8-4 is a Garratt articulated locomotive. The wheel arrangement is effectively two 4-8-0 locomotives operating back to back, with the boiler and cab suspended between the two engine units. Each engine unit has two pairs of leading wheels in a leading bogie, followed by four coupled pairs of driving wheels and no trailing wheels. Since the 4-8-0 type is known as a Mastodon type, the corresponding Garratt type would be referred to as a Double Mastodon. A similar wheel arrangement exists for Mallet locomotives, but is referred to as 4-8-8-4.

A Triplex locomotive is a steam locomotive that divides the driving force on its wheels by using three pairs of cylinders rigidly mounted to a single locomotive frame. Inevitably any such locomotive will be articulated. All the examples that have been produced have been of the Mallet type but with one extra set of driving wheels under the tender.

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