The UIC classification of locomotive axle arrangements^[1] describes the wheel arrangement of locomotives, multiple units and trams. It is set out in the International Union of Railways (UIC) "Leaflet 650 - Standard designation of axle arrangement on locomotives and multiple-unit sets". It is used in much of the world. The United Kingdom used a related scheme. The United States uses the simplified AAR wheel arrangement for modern locomotives.

Examples

• Bo'Bo' (UK Bo-Bo) Two bogies or wheel assemblies under the unit. Each bogie has two powered axles individually driven by traction motors
• Co'Co' (UK Co-Co) Two bogies or wheel assemblies under the unit. Each bogie has three powered axles individually driven by traction motors
• Co'Bo' (UK Co-Bo) Two bogies or wheel assemblies under the unit. One bogie has three powered axles and the other bogie has two powered axles. All axles are individually driven by traction motors