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

thumb|upright|Whyte notation from a handbook for railroad industry workers published in 1906

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, 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.

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 . 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. 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.

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:

{|class="wikitable"

!Suffix

!Meaning

!Example

|-

|[No Suffix]

|Tender locomotive

|

|-

|T

|Tank locomotive

|

|-

|ST

|Saddle tank locomotive

|

|-

|WT

|Well tank locomotive

|

|-

|PT

|Pannier tank locomotive

|

|-

|C or CT

|Crane tank locomotive

|

|-

|IST

|Inverted saddle tank locomotive

|

|-

|T+T (or ST+T, WT+T, etc.)

|Tender-tank locomotive

|

|-

|WT

|Wing tank locomotive

|0-4-0WT

|-

|RT

|Rear tank locomotive

|0-4-4RT

|}

Other steam locomotives

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

|-

| 45px || 2-2-4 || Aerolite

|-

| 40px || 4-2-0 || Jervis

|-

| 50px || 4-2-2 || Bicycle

|-

| colspan="4" |

|-

| 35px || 0-4-0 || Four-wheel switch

|-

| 60px || 2-4-2 || Columbia eight-wheeler

|-

| 70px || 4-4-2 || Atlantic

|-

| 75px || 4-4-4 || Reading, Jubilee (Canada)

|-

| colspan="4" |

|-

| 55px || 0-3-0<!--this is correct-->||(one driving wheel per axle; used on Patiala State Monorail Trainways and also on the Listowel and Ballybunion Railway)

|-

| 55px || 0-6-0 || Six-coupled, || 11,000

|-

| 75px || 2-6-2 || Prairie (not Britain)

|-

| 80px || 4-6-2 || Pacific || 6,800

|-

| 85px || 4-6-4 || Hudson, Baltic

|-

| || 4-6-6 || Use on the Boston and Albany Railroad.

|-

| colspan="4" |

|-

| 80px || 0-8-0 || Eight-coupled || 35,000

|-

| 95px || 2-8-2 || Mikado,

|-

| 100px || 2-8-4 || Berkshire, Kanawha

|-

| 105px || 2-8-6 || Used only on four Mason Bogie locomotives

|-

| 100px || 4-8-0 || Twelve Wheeler, Mastodon Mohawk (NYC)

|-

| 120px || 4-8-4 || Northern, Niagara, Confederation, Dixie, Greenbrier, Pocono, Potomac, Heavy Mountain (Atchison, Topeka, and Santa Fe), Golden State (Southern Pacific), Western, Laurentian (Delaware & Hudson Railroad), General, Wyoming (Lehigh Valley), Governor, Big Apple, GS Series "Daylight" (Southern Pacific) Ten-wheel switch Russian Decapod

|-

| 110px || 2-10-2 || Santa Fe

|-

||| 2-10-6 || Proposed by Indian Railways, never built

|-

| 110px || 4-10-0 || Mastodon Southern Pacific, Overland, Super Mountain

|88

|-

| colspan="4" |

|-

| 150px || 4-14-4 || AA20, Soviet

|-

| || 2-4-6-2 ||

|

|-

| || 4-4-4-2 || Planned for proposed ACE 3000 locomotive.

|-

| 115px || 4-4-4-4 || (PRR T1)

|53

|-

| 130px || 6-4-4-6 || (PRR S1) || 1

|-

| 130px || 4-4-6-4 || (PRR Q2) || 26

|-

| 130px || 4-6-4-4 || (PRR Q1) || 1

|-

| colspan="4" |

|-

! colspan="4" | Articulated locomotives (simple and compound)

|-

| colspan="4" |

|-

| 80px || 0-4-4-0 ||

|-

| 45px 38px || 2-4-4-0 ||

|5

|-

| 38px 45px || 0-4-4-2 ||

|-

| 100px || 2-4-4-2 ||Little River

|-

| <!-- 100px --> || 4-4-6-2 || Used by the Santa Fe || 2

|-

|

|0-6-4-0

|Used on Engerth articulated locomotives

|4

|-

| 115px || 0-6-6-0 ||

|-

| 120px || 2-6-6-0 ||

|-

| 125px || 2-6-6-2 ||

|1,300

|-

| 135px || 2-6-6-4 || || 60

|-

| 140px || 2-6-6-6 || Allegheny, Blue Ridge || 68

|-

| 135px || 4-6-6-2 || (Southern Pacific class AM-2)

|-

| 140px || 4-6-6-4 || Challenger || 252

|-

| colspan="4" |

|-

| || 0-8-6-0

|-

| colspan="4" |

|-

| 135px || 2-6-8-0 || (Southern Railway, Great Northern Railway)

|39

|-

| colspan="4" |

|-

| 145px || 0-8-8-0 || Angus

|-

| 150px || 2-8-8-0 || Bull Moose

|-

| 160px || 2-8-8-2 ||Chesapeake

|222

|-

| 165px || 2-8-8-4 || Yellowstone || 78

|-

| 165px || 4-8-8-2 ||Cab Forward || 195

|-

| 170px || 4-8-8-4 || Big Boy || 25

|-

| colspan="4" |

|-

| 185px || 2-10-10-2 || (Santa Fe and Virginian railroads) || 1

|-

| colspan="4" |

|-

! colspan="4" | Garratt articulated locomotives

|-

| colspan="4" |

|-

| 75px || 0-4-0+0-4-0 ||

|-

| x18px || 0-6-0+0-6-0 ||

|-

| x18px || 2-4-0+0-4-2 ||

|-

| x18px || 2-4-2+2-4-2 ||

|-

| x18px || 2-6-0+0-6-2 ||

|-

| x18px || 2-6-2+2-6-2 || Double Prairie

|-

| x18px || 2-8-0+0-8-2 ||

|-

| x17px || 2-8-2+2-8-2 || Double Mikado

|-

| x18px || 4-4-2+2-4-4 ||

|-

| x18px || 4-6-0+0-6-4 ||

|-

| x17px || 4-6-2+2-6-4 || Double Pacific

|-

| x18px || 4-6-4+4-6-4 || Double Hudson

|-

| x18px || 4-8-0+0-8-4 ||

|-

| x18px || 4-8-2+2-8-4 ||

|-

| x18px || 4-8-4+4-8-4 ||

|}

See also

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

References

Further reading

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