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Inrail transport, awheel arrangement orwheel configuration is a system of classifying the way in which wheels are distributed under alocomotive.[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 assteam,electric, anddiesel 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.
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The main notations are theWhyte notation (based on counting the wheels), theAAR wheel arrangement notation (based on counting either the axles or thebogies), and theUIC classification of locomotive axle arrangements (based on counting either the axles or the bogies).
The Whyte notation is generally used forsteam locomotives throughout theUnited States,Canada, theUnited Kingdom andIreland. 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 mainlandEurope, the UIC classification scheme is generally used for all locomotive types including steam, with some exceptions. InFrance, 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 theSwiss locomotive and railcar classification now only retained for itsnarrow-gauge railways.
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| VDEV/VMEV/UIC-system | Whyte-notation | American name | Picture scheme Locomotive front is to the left |
|---|---|---|---|
| A1 | 0-2-2 | Northumbrian |  |
| A2 | 0-2-4 | ||
| 1A | 2-2-0 | Planet |  |
| 1A1 | 2-2-2 | Single, Jenny Lind, Patentee |  |
| 1A2 | 2-2-4 | Aerolite |  |
| 2′A | 4-2-0 | Jervis |  |
| 2′A1 | 4-2-2 |  | |
| 2A2 | 4-2-4 | Huntington |  |
| 3A | 6-2-0 | Crampton |  |
| N/A | 0-3-0 |  | |
| B | 0-4-0 | Four-Wheel-Switcher |  |
| B1 | 0-4-2 | Olomana |  |
| B2′ | 0-4-4 | Forney four-coupled |  |
| B3′ | 0-4-6 | ||
| 1B | 2-4-0 | Porter |  |
| 1′B1′ | 2-4-2 | Columbia |  |
| 1B2′ | 2-4-4 | Forney, Mason Bogie |  |
| 1B3′ | 2-4-6 | ||
| 2′B | 4-4-0 | American, Eight-Wheeler |  |
| 2′B1′ | 4-4-2 | Atlantic |  |
| 2′B2′ | 4-4-4 | Jubilee (CA), Reading (US) |  |
| 2′B3′ | 4-4-6 | ||
| C | 0-6-0 | Six-Wheel-Switcher | |
| C1 | 0-6-2 | Webb, Branchline |  |
| C2′ | 0-6-4 |  | |
| 1′C | 2-6-0 | Mogul |  |
| [[1′C1′]] | 2-6-2 | Prairie |  |
| 1′C2′ | 2-6-4 | Adriatic, Lionel |  |
| 1′C3′ | 2-6-6 |  | |
| 2′C | 4-6-0 | Ten-Wheeler |  |
| 2′C1′ | 4-6-2 | Pacific |  |
| 2′C2′ | 4-6-4 | Hudson (NYC), Baltic (MR), Shore Line (NH) |  |
| D | 0-8-0 | Eight-Wheel-Switcher |  |
| D1 | 0-8-2 | Transfer |  |
| D2′ | 0-8-4 |  | |
| D3′ | 0-8-6 | ||
| 1′D | 2-8-0 | Consolidation |  |
| 1′D1′ | 2-8-2 | Mikado, MacArthur (USATC) |  |
| 1′D2′ | 2-8-4 | Berkshire, Kanawha (C&O), Lima (B&M)&(IC) |  |
| 1′D3′ | 2-8-6 |  | |
| 2′D | 4-8-0 | Twelve-Wheeler, Mastodon |  |
| 2′D1′ | 4-8-2 | Mountain, Mohawk (NYC), New Haven (NH) |  |
| 2′D2′ | 4-8-4 | Northern, General Service (SP), Golden State (SP), Niagara (NYC), Wyoming (LV), Potomac (WM), Confederation (CN), Dixie (NC&St.L), Greenbrier (C&O), Laurentian (D&H), Montana (GN), Pocono (Lackawanna), |  |
| 2D3 | 4-8-6 |  | |
| 3′D3′ | 6-8-6 | Turbine (Pennsylvania Railroad Steam Turbine) |  |
| E | 0-10-0 | Ten-Wheel Switcher |  |
| E1′ | 0-10-2 | Union |  |
| 1′E | 2-10-0 | Decapod |  |
| 2′E | 4-10-0 | Mastodon, El Gobernador, |  |
| 1′E1′ | 2-10-2 | Santa Fe, Decapod (SP), Central (IC) |  |
| 1′E2′ | 2-10-4 | Texas, Selkirk (CP), Colorado (CB&Q) |  |
| 2′E1′ | 4-10-2 | Southern Pacific, Overland (UP) |  |
| F | 0-12-0 | Pennsylvania, Twelve-Wheel-Switcher |  |
| 1′F | 2-12-0 | Centipede |  |
| 1′F1′ | 2-12-2 | Javanic |  |
| 2′F1′ | 4-12-2 | Union Pacific |  |
| 2′G2′ | 4-14-4 | Soviet (AA) |  |
| A′A | 0-2-2-0 | ||
| B′B | 0-4-4-0 | nameless (Mallet) | |
| B′B1 | 0-4-4-2 | nameless (Mallet) | |
| 2′BB2′ | 4-4-4-4 | nameless (Pennsylvania Railroad Duplex) |  |
| 3′BB3′ | 6-4-4-6 |  | |
| 2′CB2′ | 4-6-4-4 | nameless (Pennsylvania Railroad Duplex) |  |
| C′C | 0-6-6-0 | Old Maude (Mallet) |  |
| (1′C)C | 2-6-6-0 | nameless (Mallet) |  |
| (1′C)C1′ | 2-6-6-2 | nameless (Mallet) |  |
| (1′C)C2′ | 2-6-6-4 | nameless (Simple articulated) |  |
| (2′C)C2′ | 4-6-6-4 | Challenger (Simple articulated) |  |
| (1′C)C3′ | 2-6-6-6 | Allegheny, Blue Ridge (Simple articulated) |  |
| D′D | 0-8-8-0 | Angus (Mallet) |  |
| (1′D)D | 2-8-8-0 | Bull Moose (Mallet) |  |
| (1′D)D1′ | 2-8-8-2 | Chesapeake (C&O), Cab Forward (SP) (Mallet) |  |
| (1′D)D2′ | 2-8-8-4 | Yellowstone (Simple articulated) |  |
| (2′D)D1′ | 4-8-8-2 | Cab Forward (Simple articulated) |  |
| (2′D)D2′ | 4-8-8-4 | Big Boy (Simple articulated) |  |
| (1′E)E1′ | 2-10-10-2 | Virginian (Mallet) |  |
| (1′D1′)(1′D1′) | 2-8-2+2-8-2 | Nameless,Garratt |  |
| (2′C1′)(1′C2′) | 4-6-2+2-6-4 | nameless (Garratt) |  |
| (2′C2′)(2′C2′) | 4-6-4+4-6-4 | nameless (Garratt) |  |
| (2′D)(D2′) | 4-8-0+0-8-4 | nameless (Garratt) | |
| (2′D1′)(1′D2′) | 4-8-2+2-8-4 | Double Mountain (Garratt) |  |
| (2′D2′)(2′D2′) | 4-8-4+4-8-4 | nameless (Garratt) |  |
Geared steam locomotives such asShays,Heislers, andClimaxes do not have a standard wheel arrangement classification system. Instead of being classified by wheel arrangement, they are instead classified by their design and their number oftrucks.
| No. of trucks | American name | Picture scheme |
|---|---|---|
| 2-truck | Class A Shay, Class B Shay, Class A Climax, Class B Climax, Heisler | oo oo |
| 3-truck | Class C Shay, Class C Climax, Heisler | oo oo oo |
| 4-truck | Class D Shay | oo oo oo oo |
