The UIC classification of locomotive axle arrangements, sometimes known as the German classification[1] or German system,[2][3] describes the wheel arrangement of locomotives, multiple units and trams.
It is used in much of the world, notable exceptions being the United Kingdom and North America[a].
The classification system is managed by the International Union of Railways (UIC).
[4] The UIC uses the following structure:[4] Garratt 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′.