Wheel arrangement

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Locomotives of different types (Whyte and UIC wheel notation)

In rail transport, a wheel arrangement or wheel configuration is a system of classifying the way in which wheels are distributed under a locomotive.[1] Several notations exist to describe the wheel assemblies of a locomotive by type, position, and connections, with the adopted notations varying by country. Within a given country, different notations may also be employed for different kinds of locomotives, such as steam, electric, and diesel powered.

Especially in steam days, wheel arrangement was an important attribute of a locomotive because there were many different types of layout adopted, each wheel being optimised for a different use (often with only some being actually "driven"). Modern diesel and electric locomotives are much more uniform, usually with all axles driven.

Major notation schemes[edit]

The main notations are the Whyte notation (based on counting the wheels), the AAR wheel arrangement notation (based on counting either the axles or the bogies), and the UIC classification of locomotive axle arrangements (based on counting either the axles or the bogies).

Whyte notation is generally used for steam locomotives throughout the United States, Canada, the United Kingdom and Ireland. For diesels and electrics, North America uses the AAR wheel arrangement scheme while British practice uses a slightly simplified form of the European UIC classification scheme (except for small diesel shunters, where Whyte notation is used).

In mainland Europe, the UIC classification scheme is generally used for all locomotive types including steam, with some exceptions. In France, the UIC classification is used for diesels and electrics while a scheme similar to the Whyte notation, but counting axles instead of wheels, is used for steam locomotives. Notably, Switzerland had its own separate notation system until 1989, with the Swiss locomotive and railcar classification now only retained for its narrow gauge railways.

  • AAR wheel arrangement - Used largely throughout the US and Canada for diesel and electric locomotives.
  • UIC classification - Used in mainland Europe for all locomotive types. Used in the UK for electric and large diesel locomotives.
  • Whyte notation - Used in North America, the UK and Ireland for steam locomotives, and for shunter locomotives (US: switcher locomotives) in the UK.

Comparison of wheel arrangements and wheel picture[edit]

VDEV/VMEV/UIC-System Whyte-Notation American name Picture scheme
Locomotive front is to the left
A1 0-2-2 Oo
A2 0-2-4 Ooo
1A 2-2-0 Planet oO
1A1 2-2-2 Patentee oOo
1A2 2-2-4 oOoo
2A 4-2-0 Crampton, Norris, Jervis ooO
2A1 4-2-2 Single Driver ooOo
2A2 4-2-4 ooOoo
3A 6-2-0 Crampton oooO
N/A 0-3-0 OOO
B 0-4-0 Four-Wheel-Switcher OO
B1 0-4-2 OOo
B2 0-4-4 Forney OOoo
B3 0-4-6 OOooo
1B 2-4-0 Hanscom oOO
1B1 2-4-2 Columbia oOOo
1B2 2-4-4 oOOoo
1B3 2-4-6 oOOooo
2B 4-4-0 American, Eight-Wheeler ooOO
2B1 4-4-2 Atlantic ooOOo
2B2 4-4-4 Jubilee (CA), Reading (US) ooOOoo
2B3 4-4-6 ooOOooo
C 0-6-0 Six-Wheel-Switcher OOO
C1 0-6-2 OOOo
C2 0-6-4 OOOoo
1C 2-6-0 Mogul oOOO
[[1C1]] 2-6-2 Prairie oOOOo
1C2 2-6-4 Adriatic oOOOoo
1C3 2-6-6 oOOOooo
2C 4-6-0 Ten-Wheeler ooOOO
2C1 4-6-2 Pacific ooOOOo
2C2 4-6-4 Hudson, Baltic ooOOOoo
D 0-8-0 Eight-Wheel-Switcher OOOO
D1 0-8-2 OOOOo
D2 0-8-4 OOOOoo
D3 0-8-6 OOOOooo
1D 2-8-0 Consolidation oOOOO
1D1 2-8-2 Mikado oOOOOo
1D1 2-8-2T MacArthur oOOOOo
(1D1)(1D1) 2-8-2+2-8-2 Double Mikado, Garratt oOOOOo+oOOOOo
1D2 2-8-4 Berkshire oOOOOoo
1D3 2-8-6 oOOOOooo
2D 4-8-0 Twelve-Wheeler, Mastodon ooOOOO
2D1 4-8-2 Mountain, Mohawk (NYC) ooOOOOo
2D2 4-8-4 Northern, General Service (SP), Golden State (SP), Niagara (NYC), Wyoming ooOOOOoo
2D3 4-8-6 ooOOOOooo
3D3 6-8-6 Turbine (Pennsylvania Railroad Steam Turbine) oooOOOOooo
E 0-10-0 Ten-Wheel Switcher OOOOO
E1 0-10-2 Union OOOOOo
1E 2-10-0 Decapod oOOOOO
2E 4-10-0 Mastodon ooOOOOO
1E1 2-10-2 Santa Fe oOOOOOo
1E2 2-10-4 Texas, Selkirk (Canadian Pacific) oOOOOOoo
2E1 4-10-2 Southern Pacific, Overland ooOOOOOo
F 0-12-0 Pennsylvania, Twelve-Wheel-Switcher OOOOOO
1F 2-12-0 Centipede oOOOOOO
1F1 2-12-2 Javanic oOOOOOOo
2F1 4-12-2 Union Pacific ooOOOOOOo
2G2 4-14-4 ooOOOOOOOoo
Soviet (AA) 0-2-2-0 O O
BB 0-4-4-0 nameless (Mallet) OO OO
BB1 0-4-4-2 nameless (Mallet) OO OOo
2BB2 4-4-4-4 nameless (Pennsylvania Railroad Duplex) ooOO OOoo
3BB3 6-4-4-6 oooOO OOooo
2CB2 4-6-4-4 nameless (Pennsylvania Railroad Duplex) ooOOO OOoo
CC 0-6-6-0 Erie (Mallet) OOO OOO
(1C)C 2-6-6-0 Denver (Mallet) oOOO OOO
(1C)C1 2-6-6-2 Mallet Mogul (SP), Prairie Mallet (ATSF), Chesapeake oOOO OOOo
(1C)C2 2-6-6-4 nameless (Simple articulated) oOOO OOOoo
(2C)C2 4-6-6-4 Challenger (Simple articulated) ooOOO OOOoo
(1C)C3 2-6-6-6 Allegheny, Blue Ridge (Mallet/Simple articulated) oOOO OOOooo
DD 0-8-8-0 Angus (Mallet) OOOO OOOO
(1D)D 2-8-8-0 Bullmoose (Mallet) oOOOO OOOO
(1D)D1 2-8-8-2 Chesapeake, Mallet consolidation (Mallet) oOOOO OOOOo
(1D)D2 2-8-8-4 Yellowstone (Mallet/Simple articulated) oOOOO OOOOoo
(2D)D1 4-8-8-2 Cab Forward (Simple articulated) ooOOOO OOOOo
(2D)D2 4-8-8-4 Big Boy (Simple articulated) ooOOOO OOOOoo
(1E)E1 2-10-10-2 Virginian (Mallet) oOOOOO+OOOOOo
(2C1)(1C2) 4-6-2+2-6-4 Double Pacific (Garratt) ooOOOo+oOOOoo
(2C2)(2C2) 4-6-4+4-6-4 Double Hudson (Garratt) ooOOOoo+ooOOOoo
(2D)(D2) 4-8-0+0-8-4 Double Mastodon (Garratt) ooOOOO+OOOOoo
(2D1)(1D2) 4-8-2+2-8-4 Double Mountain (Garratt) ooOOOOo+oOOOOoo
(2D2)(2D2) 4-8-4+4-8-4 Double Northern (Garratt) ooOOOOoo+ooOOOOoo

See also[edit]


  1. ^ "Wheel Arrangements". Railway Technical Web Pages. 1 August 2011. Retrieved 1 August 2011.