Class (locomotive)
Encyclopedia
Class refers to a group of locomotives built to a common design for a single railroad. Often members of a particular class had detail variations between individual examples, and these could lead to subclasses. Sometimes technical alterations (especially rebuilding, superheating, re-engining, etc.) move a locomotive from one class to another. Different railways had different systems, and sometimes one railway (or its successors) used different systems at different times and for different purposes, or applied those classifications inconsistently. Sometimes therefore it is not clear where one class begins and another ends. The result is a classic example of the Lumper splitter problem
.
grouped its roster into four classes before the Civil War
, though they had by that point dozens of different designs.
Later classes were based on design. A group of locomotives built off the same blueprints constituted a class, and if some of the locomotives in the class were sufficiently modified, a new class might be established for the modified examples. When electric locomotives were introduced, the same scheme was applied to them.
Since steam and early electric locomotives were usually custom built, classes were assigned by the railroad, and each railroad had its own system. Mergers of lines and sales of locomotives brought about changes of class. Early diesels were often fitted into the locomotive class system, but since they were generally not custom built the use of manufacturer model designations overtook the class system and made it irrelevant, except for historical discussion.
and was usually coded by a letter of the alphabet. Different railroads used different codes, so that "J" on the New York Central Railroad
meant a 4-6-4
(Hudson), while on the Norfolk and Western Railway
it mean a 4-8-4
(Northern), and on the Baltimore and Ohio Railroad
it denoted a 4-4-0
with a Wootten firebox
.
Articulated locomotives were handled through two different methods. On many railroads each wheel arrangement was assigned its own unique letter, due to the limited number of arrangements that had to be represented. On other railroads this was insufficient, and commonly articulated locomotives were represented with a two letter code, one letter for the arrangement of each half. Therefore the Pennsylvania Railroad GG1 (UIC
2Co+Co2) is represented as if it were two ten-wheelers (4-6-0
) coupled tail-to-tail.
locomotives on the B&O
, labelled "S" and "S-1".
used a "s" suffix to indicate superheating
, while on the B&O
a "t" suffix indicated an engine with an oversize tender
.
The old railway companies had various systems of classification. Taking the "Big Four" companies which operated from 1923 to 1947:
and the "Q" Class was also a 0-6-0. See:
was given a letter (e.g. A for 4-6-2, B for 4-6-0, etc.) and this was followed by a number denoting the class (e.g. A1, B1, etc.).
Lumpers and splitters
Lumping and splitting refers to a well-known problem in any discipline which has to place individual examples into rigorously defined categories. The lumper/splitter problem occurs when there is the need to create classifications and assign examples to them, for example schools of literature,...
.
Development
As locomotives became more numerous the need arose to deal with them in groups of similar engines rather than as named or numbered individuals. These groups were named "classes" and at first tended to reflect capability rather than design. For example, the Baltimore and Ohio RailroadBaltimore and Ohio Railroad
The Baltimore and Ohio Railroad was one of the oldest railroads in the United States and the first common carrier railroad. It came into being mostly because the city of Baltimore wanted to compete with the newly constructed Erie Canal and another canal being proposed by Pennsylvania, which...
grouped its roster into four classes before the Civil War
American Civil War
The American Civil War was a civil war fought in the United States of America. In response to the election of Abraham Lincoln as President of the United States, 11 southern slave states declared their secession from the United States and formed the Confederate States of America ; the other 25...
, though they had by that point dozens of different designs.
Later classes were based on design. A group of locomotives built off the same blueprints constituted a class, and if some of the locomotives in the class were sufficiently modified, a new class might be established for the modified examples. When electric locomotives were introduced, the same scheme was applied to them.
Since steam and early electric locomotives were usually custom built, classes were assigned by the railroad, and each railroad had its own system. Mergers of lines and sales of locomotives brought about changes of class. Early diesels were often fitted into the locomotive class system, but since they were generally not custom built the use of manufacturer model designations overtook the class system and made it irrelevant, except for historical discussion.
Class system organization
Usually the class system for a railroad was built on a simply hierarchy which assigned each class a code.First level: Wheel arrangement
The first level was usually for the wheel arrangementWheel arrangement
In rail transport, a wheel arrangement is a system of classifying the way in which wheels are distributed beneath a locomotive.. Several notations exist to describe the wheel assemblies of a locomotive by type, position, and connections, with the adopted notations varying by country...
and was usually coded by a letter of the alphabet. Different railroads used different codes, so that "J" on the New York Central Railroad
New York Central Railroad
The New York Central Railroad , known simply as the New York Central in its publicity, was a railroad operating in the Northeastern United States...
meant a 4-6-4
4-6-4
Under the Whyte notation for the classification of steam locomotives, 4-6-4 represents the wheel arrangement of four leading wheels on two axles , six powered and coupled driving wheels on three axles, and four trailing wheels on two axles .Other equivalent classifications are:UIC classification:...
(Hudson), while on the Norfolk and Western Railway
Norfolk and Western Railway
The Norfolk and Western Railway , a US class I railroad, was formed by more than 200 railroad mergers between 1838 and 1982. It had headquarters in Roanoke, Virginia for most of its 150 year existence....
it mean a 4-8-4
4-8-4
Under the Whyte notation classification of steam locomotives, 4-8-4 represents the wheel arrangement of four leading wheels on two axles , eight powered and coupled driving wheels on four axles, and four trailing wheels on two axles .Other equivalent classifications are:UIC classification: 2D2...
(Northern), and on the Baltimore and Ohio Railroad
Baltimore and Ohio Railroad
The Baltimore and Ohio Railroad was one of the oldest railroads in the United States and the first common carrier railroad. It came into being mostly because the city of Baltimore wanted to compete with the newly constructed Erie Canal and another canal being proposed by Pennsylvania, which...
it denoted a 4-4-0
4-4-0
Under the Whyte notation for the classification of steam locomotives, 4-4-0 represents the wheel arrangement of four leading wheels on two axles , four powered and coupled driving wheels on two axles, and no trailing wheels...
with a Wootten firebox
Wootten firebox
The Wootten firebox is a type of firebox used on steam locomotives. The firebox was very wide to allow combustion of anthracite coal waste, known as Culm. Its size necessitated unusual placement of the crew, examples being camelback locomotives...
.
Articulated locomotives were handled through two different methods. On many railroads each wheel arrangement was assigned its own unique letter, due to the limited number of arrangements that had to be represented. On other railroads this was insufficient, and commonly articulated locomotives were represented with a two letter code, one letter for the arrangement of each half. Therefore the Pennsylvania Railroad GG1 (UIC
International Union of Railways
The UIC , or International Union of Railways, is an international rail transport industry body.- Brief history :The railways of Europe originated as separate concerns. There were many border changes after World War I and the Treaty of Versailles. Colonial railways were the responsibility of the...
2Co+Co2) is represented as if it were two ten-wheelers (4-6-0
4-6-0
Under the Whyte notation for the classification of steam locomotives, 4-6-0 represents the wheel arrangement of four leading wheels on two axles in a leading truck, six powered and coupled driving wheels on three axles, and no trailing wheels. This wheel arrangement became the second-most popular...
) coupled tail-to-tail.
Second level: Sequential model
A sequence number was often added to distinguish different designs of the same wheel arrangement. As a rule the first design for a given arrangement had no sequence number, so that numbering stated at 1 with the second design for the wheel arrangement. For example, there were two main classes of 2-10-22-10-2
Under the Whyte notation for the classification of steam locomotives, 2-10-2 represents the wheel arrangement of two leading wheels on one axle, usually in a leading truck, ten powered and coupled driving wheels on five axles, and two trailing wheels on one axle, usually in a trailing truck...
locomotives on the B&O
Baltimore and Ohio Railroad
The Baltimore and Ohio Railroad was one of the oldest railroads in the United States and the first common carrier railroad. It came into being mostly because the city of Baltimore wanted to compete with the newly constructed Erie Canal and another canal being proposed by Pennsylvania, which...
, labelled "S" and "S-1".
Third level: Variants
Letter suffixes were often used to indicate variants in a basic design. Sometimes these also referred to specific characteristics; for example, for many years the Pennsylvania RailroadPennsylvania Railroad
The Pennsylvania Railroad was an American Class I railroad, founded in 1846. Commonly referred to as the "Pennsy", the PRR was headquartered in Philadelphia, Pennsylvania....
used a "s" suffix to indicate superheating
Superheating
In physics, superheating is the phenomenon in which a liquid is heated to a temperature higher than its boiling point, without boiling...
, while on the B&O
Baltimore and Ohio Railroad
The Baltimore and Ohio Railroad was one of the oldest railroads in the United States and the first common carrier railroad. It came into being mostly because the city of Baltimore wanted to compete with the newly constructed Erie Canal and another canal being proposed by Pennsylvania, which...
a "t" suffix indicated an engine with an oversize tender
Tender locomotive
A tender or coal-car is a special rail vehicle hauled by a steam locomotive containing the locomotive's fuel and water. Steam locomotives consume large quantities of water compared to the quantity of fuel, so tenders are necessary to keep the locomotive running over long distances. A locomotive...
.
Class Names
Most locomotives were given simple codes, but some classes were named, formally or not.- The Union Pacific Big BoyUnion Pacific Big BoyBig Boy was the name of the Union Pacific Railroad's 4000-class 4-8-8-4 articulated steam locomotives, built between 1941 and 1944 by American Locomotive Company...
class was said to have been given that name when it was scrawled on the smokebox of one at the factory. - The Baltimore and Ohio RailroadBaltimore and Ohio RailroadThe Baltimore and Ohio Railroad was one of the oldest railroads in the United States and the first common carrier railroad. It came into being mostly because the city of Baltimore wanted to compete with the newly constructed Erie Canal and another canal being proposed by Pennsylvania, which...
P-7 class was referred to as the "President" class because initially each locomotive had the name of a U.S. PresidentPresident of the United StatesThe President of the United States of America is the head of state and head of government of the United States. The president leads the executive branch of the federal government and is the commander-in-chief of the United States Armed Forces....
on the cab. - Also on the B&O, the S and S-1 classes were referred to as "Big Sixes" because the road numbers began with 6.
British Practice
- For recent practice see: British Rail locomotive and multiple unit numbering and classificationBritish Rail locomotive and multiple unit numbering and classificationA number of different numbering and classification schemes were used for locomotives and multiple units operated by British Railways , and this page explains the principal systems...
The old railway companies had various systems of classification. Taking the "Big Four" companies which operated from 1923 to 1947:
Great Western Railway
The class number was usually taken from the first member of each class, e.g. "5700 Class" or "57XX Class" for locomotives in the number series beginning 5700.- See: GWR locomotive numbering and classificationGWR locomotive numbering and classificationThe GWR was the longest-lived of the pre-nationalisation railway companies in Britain, surviving the 'Grouping' of the railways in 1923 almost unchanged. As a result, the history of its numbering and classification of locomotives is relatively complicated...
Southern Railway
Each class was given a letter or number but these were not very meaningful. For example, the "700" Class was a 0-6-00-6-0
Under the Whyte notation for the classification of steam locomotives, 0-6-0 represents the wheel arrangement of no leading wheels, six powered and coupled driving wheels on three axles, and no trailing wheels...
and the "Q" Class was also a 0-6-0. See:
- SR locomotive numbering and classificationSR locomotive numbering and classificationA number of different numbering and classification schemes were used for the locomotives owned by the Southern Railway and its constituent companies...
- SR multiple unit numbering and classificationSR multiple unit numbering and classificationThe Southern Railway created classification and numbering systems for its large fleet of electric multiple units that were perpetuated by the Southern Region of British Rail until the early 1980s, when the impact of TOPS was felt...
London, Midland and Scottish Railway
Each locomotive was given a power classification, e.g. "3F". However, many different classes would have the same power classification so this was not helpful for identifying classes.- See: LMS locomotive numbering and classificationLMS locomotive numbering and classificationA number of different numbering and classification schemes were used for the locomotives owned by the London, Midland and Scottish Railway and its constituent companies; this page explains the principal systems that were used....
London and North Eastern Railway
The LNER's classification system was the most helpful to railway enthusiasts. Each wheel arrangementWhyte notation
The Whyte notation for classifying steam locomotives by wheel arrangement was devised by Frederick Methvan Whyte and came into use in the early twentieth century encouraged by an editorial in American Engineer and Railroad Journal...
was given a letter (e.g. A for 4-6-2, B for 4-6-0, etc.) and this was followed by a number denoting the class (e.g. A1, B1, etc.).
- See: LNER locomotive numbering and classificationLNER locomotive numbering and classificationA number of different numbering and classification schemes were used for the locomotives owned by the London and North Eastern Railway and its constituent companies. This page explains the principal systems that were used...
See also
- Baltimore and Ohio Railroad locomotivesBaltimore and Ohio Railroad locomotivesOn the Baltimore and Ohio Railroad, locomotives were always considered of great importance, and the railroad was involved in many experiments and innovations.-Early locomotives:...
- PRR locomotive classificationPRR locomotive classificationLocomotive classification on the Pennsylvania Railroad took several forms. Early on, steam locomotives were given single-letter classes. As the 26 letters were quickly assigned, that scheme was abandoned for a more complex system...
- Locomotives of New ZealandLocomotives of New ZealandLocomotives of New Zealand currently in operation owned by KiwiRail consist of 172 diesel-electric locomotives, 22 electric locomotives, 3 railcars, and 103 shunting locomotives...