The UIC classification is a system for explaining the wheel arrangement of diesel locomotives, electric locomotives, and multiple-units.
The system was developed by the International Union of Railways; its acronym comes from the French: Union Internationale des Chemins de fer meaning the same. It was developed to be superior to the Whyte notation which cannot classify every arrangement type properly.
The system has a lot more rules than the Whyte Notation:
- Capital letters denote powered axles. A = 1 powered axle; B = 2; C = 3 etc.
- The lower case letter 'o' denote separately powered axles: so a Bo truck (bogie) would have two separately powered axles.
- Numbers denote a non-powered axle. So 1 = one non-powered axle; 2 = two non-powered axles etc.
- An apostrophe ( ' ) separates trucks (bogies).
- A plus sign (+) shows completely separate mechanical systems, as in Multiple Unit.
- Brackets "()" show the separate trucks (bogies) in certain arrangements. Therefore an apostrophe wouldn't be used in that case.
- Co'Co' = Six axles;
- Bo'Bo' = Four axles;
- Do'Do' = Eight axles;
- A1A'A1A' = Two trucks with unpowered axles between them
- Bo'Bo'+Bo'Bo' = As in semi-permanently coupled carriages in a Trainset.
- Bo'Co' = Four axles at the front, six in the rear
- Co'Bo' = Six axles in the front truck and four in the rear.
- (D)(D) = Shows that the body of the locomotive is articulated, as in a rail crane.
- The "Pacific" axle arrangement under the Whyte notation is 4-6-2. Under the UIC classification this would be: 2'C1'.
- The "Big Boy" articulated is 4-8-8-4 under the Whyte system. Under the UIC classification it is: 2'(D)D2'.