
In
rail transport
Rail transport (also known as train transport) is a means of transport using wheeled vehicles running in railway track, tracks, which usually consist of two parallel steel railway track, rails. Rail transport is one of the two primary means of ...
, a wheel arrangement or wheel configuration is a system of classifying the way in which wheels are distributed under a
locomotive
A locomotive is a rail transport, rail vehicle that provides the motive power for a train. Traditionally, locomotives pulled trains from the front. However, Push–pull train, push–pull operation has become common, and in the pursuit for ...
.
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
Steam is water vapor, often mixed with air or an aerosol of liquid water droplets. This may occur due to evaporation or due to boiling, where heat is applied until water reaches the enthalpy of vaporization. Saturated or superheated steam is inv ...
,
electric
Electricity is the set of physical phenomena associated with the presence and motion of matter possessing an electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described by Maxwel ...
, 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
The main notations are the
Whyte notation (based on counting the wheels), the
AAR wheel arrangement
The AAR wheel arrangement system is a method of classifying locomotive
A locomotive is a rail transport, rail vehicle that provides the motive power for a train. Traditionally, locomotives pulled trains from the front. However, Push–pu ...
notation (based on counting either the axles or the
bogie
A bogie ( ) (or truck in North American English) comprises two or more Wheelset (rail transport), wheelsets (two Railroad wheel, wheels on an axle), in a frame, attached under a vehicle by a pivot. Bogies take various forms in various modes ...
s), and the
UIC classification of locomotive axle arrangements (based on counting either the axles or the bogies).
The Whyte notation is generally used for
steam locomotive
A steam locomotive is a locomotive that provides the force to move itself and other vehicles by means of the expansion of steam. It is fuelled by burning combustible material (usually coal, Fuel oil, oil or, rarely, Wood fuel, wood) to heat ...
s throughout the
United States
The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...
,
Canada
Canada is a country in North America. Its Provinces and territories of Canada, ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, making it the world's List of coun ...
, the
United Kingdom
The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Northwestern Europe, off the coast of European mainland, the continental mainland. It comprises England, Scotlan ...
and
Ireland
Ireland (, ; ; Ulster Scots dialect, Ulster-Scots: ) is an island in the North Atlantic Ocean, in Northwestern Europe. Geopolitically, the island is divided between the Republic of Ireland (officially Names of the Irish state, named Irelan ...
. For diesels and electrics,
North America
North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...
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
Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...
, the UIC classification scheme is generally used for all locomotive types including steam, with some exceptions. In
France
France, officially the French Republic, is a country located primarily in Western Europe. Overseas France, Its overseas regions and territories include French Guiana in South America, Saint Pierre and Miquelon in the Atlantic Ocean#North Atlan ...
, 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
Switzerland, officially the Swiss Confederation, is a landlocked country located in west-central Europe. It is bordered by Italy to the south, France to the west, Germany to the north, and Austria and Liechtenstein to the east. Switzerland ...
had its own separate notation system until 1989, with the
Swiss locomotive and railcar classification now only retained for its
narrow-gauge railway
A narrow-gauge railway (narrow-gauge railroad in the US) is a railway with a track gauge (distance between the rails) narrower than . Most narrow-gauge railways are between and .
Since narrow-gauge railways are usually built with tighter cur ...
s.
*
AAR wheel arrangement
The AAR wheel arrangement system is a method of classifying locomotive
A locomotive is a rail transport, rail vehicle that provides the motive power for a train. Traditionally, locomotives pulled trains from the front. However, Push–pu ...
- 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
Geared steam locomotives
Geared steam locomotive
A geared steam locomotive is a type of steam locomotive which uses gearing, usually reduction gearing, in the drivetrain, as opposed to the common directly driven design.
This gearing is part of the machinery within the locomotive and should not ...
s such as
Shays,
Heislers, and
Climaxes 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 of
trucks
A truck or lorry is a motor vehicle designed to transport freight, carry specialized payloads, or perform other utilitarian work. Trucks vary greatly in size, power, and configuration, but the vast majority feature body-on-frame construction ...
.
:
See also
*
Bo-Bo
B-B and Bo-Bo are the AAR wheel arrangement, Association of American Railroads (AAR) and British classifications of wheel arrangement for railway locomotives with four axles in two individual bogies. They are equivalent to the B′B′ and Bo′B ...
*
Bo-Bo-Bo
*
Co-Co locomotives
References
{{DEFAULTSORT:Wheel Arrangement
Locomotives