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Whyte notation
Locomotive wheel arrangements: leading-driving-trailing

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 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.

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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.2 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 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. 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+2-6-0.3

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 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:4

SuffixMeaningExample
[No Suffix]Tender locomotive0-6-0
TTank locomotive0-6-2T
STSaddle tank locomotive0-4-0ST
WTWell tank locomotive0-4-0WT
PTPannier tank locomotive0-6-0PT
C or CTCrane tank locomotive0-6-2CT
ISTInverted saddle tank locomotive0-4-2IST
T+T (or ST+T, WT+T, etc.)Tender-tank locomotive0-4-0T+T
WTWing tank locomotive0-4-0WT
RTRear tank locomotive0-4-4RT

Other steam locomotives

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

VB or VBTVertical boilered locomotive0-6-0VB
FFireless locomotive0-6-0F
CACompressed air locomotive0-6-0CA
RRailcar0-4-4-0R
R or RTRack locomotive0-4-0RT

Internal combustion locomotives

"8w (locomotive)" redirects here. For other uses, see 8W (disambiguation) § Rail transport.

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:6

SuffixMeaningExample
PMPetrol-mechanical locomotive4wPM
PEPetrol-electric locomotive0-6-0PE
DDiesel locomotive6wD
DMDiesel–mechanical locomotive8wDM
DEDiesel–electric locomotive0-4-0DE
DHDiesel–hydraulic locomotive0-6-0DH

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
BEBattery-electric locomotive4wBE
OEOverhead-lines electric locomotive0-8-0OE
REThird rail electric locomotive4wRE

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.) 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 classificationNameNo. of units produced
Non-articulated locomotives
0-2-2Northumbrian (after the 1830 locomotive Northumbrian)
0-2-4
2-2-0Planet
2-2-2Single,7 Jenny Lind8
2-2-4Aerolite
4-2-0Jervis9
4-2-2Bicycle10
4-2-4Huntington
6-2-0Crampton11
0-4-0Four-wheel switch12
0-4-0+4
0-4-2Olomana
0-4-4Forney13
2-4-0Porter, 'Old English'14
2-4-2Columbia15
2-4-4Forney, Mason Bogie
4-4-0American,1617 eight-wheeler
4-4-2Atlantic1819
4-4-4Reading, Jubilee (Canada)20
0-3-0(one driving wheel per axle; used on Patiala State Monorail Trainways and also on the Listowel and Ballybunion Railway)
0-6-0Six-coupled,21 Six-wheel switch,22 Bourbonnais (France - tender), Boer (France - tank)
0-6-2Branchliner, Webb
0-6-4Forney six-coupled23
0-6-6Forney six-coupled
2-6-0Mogul242511,000
2-6-2Prairie2627
2-6-4Adriatic28
2-6-6Mason Bogie
4-6-0Ten-wheeler2930 (not Britain)31
4-6-2Pacific323334356,800
4-6-4Hudson,36 Baltic37
4-6-6Use on the Boston and Albany Railroad.38
0-8-0Eight-coupled39
0-8-2Transfer
0-8-4
2-8-0Consolidation40414235,000
2-8-2Mikado,4344 Mike, MacArthur4546
2-8-4Berkshire, Kanawha4748
2-8-6Used only on four Mason Bogie locomotives
4-8-0Twelve Wheeler,4950 Mastodon51
4-8-2Mountain,5253 Mohawk (NYC)54
4-8-4Northern, Niagara, Confederation, Dixie, Greenbrier, Pocono, Potomac, Heavy Mountain (Atchison, Topeka, and Santa Fe), Golden State (Southern Pacific),55 Western, Laurentian (Delaware & Hudson Railroad), General, Wyoming (Lehigh Valley56), Governor, Big Apple, GS Series "Daylight" (Southern Pacific)57
4-8-6Proposed by Lima, never built
6-8-6Turbine, only used on the PRR S2 Steam Turbine1
0-10-0Ten-coupled,5859 Ten-wheel switch60
0-10-2Union61
2-10-0Decapod,6263 Russian Decapod
2-10-2Santa Fe64
2-10-4Texas, Colorado (CB&Q), Selkirk (Canada)65
2-10-6Proposed by Indian Railways, never built66
4-10-0Mastodon6768
4-10-2Reid Tenwheeler,6970 Southern Pacific, Overland,71 Super Mountain72
0-12-012-coupled
0-12-2Used in Argentina
2-12-0Centipede73
2-12-2Javanic7430
2-12-420
2-12-6Proposed by Lima, never built
4-12-2Union Pacific75
4-14-4AA20,76 Soviet771
Divided drive and duplex locomotives
0-2-2-0Used on the Mount Washington Cog Railway
2-2-2-0
2-2-2-2
2-2-4-01
4-2-2-0Double single78
2-4-6-2
4-4-4-2Planned for proposed ACE 3000 locomotive.
4-4-4-4(PRR T1)7953
6-4-4-6(PRR S1)801
4-4-6-4(PRR Q2)8126
4-6-4-4(PRR Q1)1
Articulated locomotives (simple and compound)
0-4-4-0
2-4-4-05
0-4-4-2
2-4-4-2Little River
4-4-6-2Used by the Santa Fe822
0-6-6-0
2-6-6-0
2-6-6-21,300
2-6-6-460
2-6-6-6Allegheny,83 Blue Ridge68
4-6-6-2(Southern Pacific class AM-2)84
4-6-6-4Challenger85252
0-8-6-0
2-6-8-0(Southern Railway, Great Northern Railway)8639
0-8-8-0Angus87
2-8-8-0Bull Moose
2-8-8-2Chesapeake222
2-8-8-4Yellowstone8878
4-8-8-2Cab Forward195
4-8-8-4Big Boy892590
2-10-10-2(Santa Fe and Virginian railroads)9120
2-8-8-8-2Triplex (Erie RR)3
2-8-8-8-4Triplex (Virginian RR)921
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+2-6-2Double Prairie
2-8-0+0-8-2
2-8-2+2-8-2Double Mikado
4-4-2+2-4-4
4-6-0+0-6-4
4-6-2+2-6-4Double Pacific
4-6-4+4-6-4Double Hudson
4-8-0+0-8-4
4-8-2+2-8-4
4-8-4+4-8-4

See also

Further reading

  • Media related to Whyte 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.

References

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