UIC classification of locomotive axle arrangements

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This article is about the UIC system of classifying locomotive axle arrangements. For the UIC system of classifying locomotives, see UIC identification marking for tractive stock.

The UIC classification of locomotive axle arrangements describes the wheel arrangement of locomotives, multiple units and trams. It is set out in the International Union of Railways (UIC) "Leaflet 650 – Standard designation of axle arrangement on locomotives and multiple-unit sets".^[1] It is used in much of the world. The United Kingdom used a related scheme. The United States uses the simplified AAR wheel arrangement for modern locomotives.

It is a more versatile system than Whyte notation, making fewer assumptions about locomotive layout. Some locomotives are impossible to classify using Whyte notation, but UIC classification handles them easily. The UIC classification is also much more suited to diesel and electric locomotives.

German classification

UIC classification is also known as German classification.^[2]

Structure

Whereas the Whyte notation counts wheels, the UIC notation counts axles.

Upper-case letters: the number of consecutive driving axles, starting at A for a single axle. C thus indicates three consecutive pairs of driving wheels.
Numbers: consecutive non-driving axles, starting with 1 for a single axle.
Lower-case "o", suffixing the driving wheel letter: axles are individually driven by separate traction motors.^[3]
Prime sign " ′ ": the axles are mounted on a bogie.
Plus sign "+": the locomotive or multiple unit consists of permanently coupled and mechanically separated individual vehicles.
Brackets: groups letters and numbers describing the same bogie. For example, (A1A) indicates a three-axle bogie with the outer two axles driven. When brackets are used a prime is not needed to indicate a bogie. Mallet locomotives can be indicated by bracketing the front power unit — for example, the Union Pacific Big Boy, 4-8-8-4 in Whyte notation, is (2′D)D2′ in UIC notation.

Garratt-type locomotives are indicated by bracketing or placing plus signs between all individual units.

Other suffixes

h: Superheated Steam (German: Heißdampf)
n: Saturated Steam (German: Nassdampf)
v: Compound (German: Verbund)
Turb: Turbine
number: number of cylinders
t: Tank locomotive
tr: tram (urban) locomotive
E: Engerth-type locomotive
G: Freight (German: Güterzug – freight train). Also used to indicate shunting locomotives
P: Passenger (German: Personenzug – passenger train)
S: Fast passenger (German: Schnellzug – express train)

The most common wheel arrangements in modern locomotives are Bo′Bo′ and Co′Co′.

Examples

(A1A)(A1A): Two bogies or wheel assemblies under the unit. Each bogie has one powered axle, one idle axle, and one more powered axle, to provide better load distribution and reduce the wheel load on the track. All powered axles are individually driven by traction motors.
BB: Four powered axles all mounted in the locomotive's frame, driven in pairs; i.e. each pair of axles is connected by driving rods or gears. Compare with "D" below.
B′B′: Two bogies or wheel assemblies under the unit. Each truck has two powered axles, connected by driving rods or gears. Three-quarters of all modern locomotives (as well as the power cars of self-propelled trains) are configured in either this or the "Bo′-Bo′" arrangement.
Bo′(A1A): Two trucks or wheel assemblies. The "Bo′" truck is under one end of the unit, and has two powered axles, while the "(A1A)" truck under the other end of the unit has one powered axle, one idle axle, and another powered axle. All powered axles are individually driven by traction motors.
Bo′Bo′: Two bogies or wheel assemblies under the unit. Each truck has two powered axles individually driven by traction motors. Three-quarters of all modern locomotives (as well as the power cars of self-propelled trains) are configured in either this or the "B′B′" arrangement. Many types of tram use this arrangement. See also: Bo-Bo.
Bo′Bo′Bo′: Three bogies or wheel assemblies under the unit. Each truck has two powered axles individually driven by traction motors. See also: Bo-Bo-Bo.
C: Three powered axles, connected by driving rods or gears, all mounted in the locomotive's frame (Whyte notation: 0-6-0).
C′C′: Two bogies or wheel assemblies under the unit. Each truck has three powered axles, connected by driving rods or gears.
Co′Co′: Two bogies or wheel assemblies under the unit. Each truck has three powered axles individually driven by traction motors. See also: Co-Co.
2Co′Co2′: A locomotive with two bogies. These have two leading axles and three individually powered axles. A number of Japanese electric locomotives used this wheel arrangement, including the JNR Class EF58 as well as the PRR GG1.
D: Four powered axles, connected by driving rods or gears, all mounted in the locomotive's frame (Whyte notation: 0-8-0).
1′D1′: One leading idle (non-driven) axle mounted in a bogie, four driven axles mounted in the frame and connected by driving rods or gears, followed one trailing idle axle mounted in a bogie (Whyte notation: 2-8-2).
E: Five powered axles, mounted in the locomotive's frame (Whyte notation: 0-10-0).
2′D1′h3S: Two front leading axles grouped in a bogie, four driving axles, one trailing axle in a bogie, simple steam expansion, superheated steam, three-cylinders, for fast trains.
1′E1′h2Gt: One front leading axle in a bogie, five driving axles, one rear trailing axle, simple steam expansion, superheated steam, two-cylinder machine, for freight trains, tank engine.
1′Dn4vP: One front leading axle in a bogie, four driving axles, saturated steam, four-cylinder machine, compound (double steam expansion), for passenger trains.
D′Dh4vtG: No front leading axle, four driving axles in a bogie, four more driven axles mounted in the frame (Mallet locomotive), superheated steam, four-cylinder machine, compound (double steam expansion), tank locomotive, for freight trains.

United Kingdom

Standard practice in the United Kingdom was to use the Whyte notation. The Southern Railway used a system modified from the UIC method. Oliver Bulleid, the Chief Mechanical Engineer, numbered his 4-6-2 Battle of Britain class Pacifics 21C XXX, referring to leading wheels, trailing wheels and finally powered wheels. The UIC classification for such a locomotive is 2′C1′, Whyte 4-6-2.

References

↑ UIC Leaflet 650. Standard designation of axle arrangement on locomotives and multiple-unit sets. [ Obligatory ]. 5th edition of 1.1.83.
↑ The Railway Data File. Published by Silverdale Books 2000. p. 52. ISBN 1-85605-499-3.
↑ This suffix is dropped in North America because nearly all North American diesels and electrics are this way.

External links

Wikimedia Commons has media related to UIC classification.

Gunter Krebs. "Wheel Arrangement". www.sktrocket.de.

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Wheel arrangement	AAR wheel arrangement UIC classification Swiss classification Whyte notation

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