UIC classification

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The wheel arrangement on large diesel locomotives is described using the UICUnion Internationale des Chemins de fer (International Union of Railways) classification system, where letters are used to describe the number of axles (as opposed to Whyte notation which describes the number of wheels). Those in use on the SVRSevern Valley Railway are as follows:

  • 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.
  • B-B: Two bogies or wheel assemblies under the unit. Each bogie has two powered axles, connected by driving rods or gears.
  • Bo-Bo: Four axles in two individual bogies, all driven by their own traction motors.
  • C: Three powered axles all mounted in the locomotive's frame, all connected by driving rods or gears.
  • C-C: Two bogies or wheel assemblies under the unit. Each bogie has three powered axles, mechanically connected by driving rods or gears.
  • Co-Co: Two six-wheeled bogies with all axles powered, with a separate motor per axle.
  • 1Co-Co1: Two eight-wheeled bogies, with three axles (six wheels) powered by separate motors for each axle, and an additional unpowered axle at the outer end of each bogie to reduce the axle load (the weight resting on each axle).

The wheel arrangement on steam locomotives and small diesel locomotives is described using Whyte notation.

Oliver BulleidOliver Vaughan Snell Bulleid, Chief Mechanical Engineer (CME) of the Southern Railway 1937-1948, the Chief Mechanical Engineer of the Southern Railway, used a modified version of the UICUnion Internationale des Chemins de fer (International Union of Railways) method to number certain of his steam locomotives. A West Country/Battle of Britain class locomotive would be numbered in a pattern 21C XXX. The first two numbers referred to the number of axles used for leading and trailing wheels, the third letter referred to the number of axles used for driving wheels using the normal UICUnion Internationale des Chemins de fer (International Union of Railways) classification substitution A=1, B=2, C=3 etc. XXX was the unique identification of the particular locomotive, hence Taw Valley entered service as 21C127.

See also

Diesel Locomotives