UIC classification of locomotive axle arrangements
The UIC classification of locomotive axle arrangements, sometimes known as the German classification or German system, describes the wheel arrangement of locomotives, multiple units and trams. It is used in much of the world, notable exceptions being the United Kingdom, which uses a slightly simplified form of UIC (except for steam locomotives and small diesel shunters, where Whyte notation is used), and in North America, where the AAR wheel arrangement system (essentially another simplification of the UIC system) is used to describe diesel and electric locomotives; Whyte notation is used in North America only  for steam locomotives. The classification system is managed by the International Union of Railways (UIC). Structure. The UIC uses the following structure: Garratt-type locomotives are indicated by bracketing or placing plus signs between all individual units. The most common wheel arrangements in modern locomotives are Bo′Bo′ and Co′Co′. Examples. The following examples are based on the UIC classification: