UIC Classification of Locomotive Axle Arrangements - Structure

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 electric traction motors.
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
  • 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′.

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