Wheel Arrangement - Major Notation Schemes

Major Notation Schemes

The main notations are the Whyte notation (based on counting the wheels), the AAR wheel arrangement notation (based on counting either the axles or the bogies), and the UIC classification of locomotive axle arrangements (based on counting either the axles or the bogies).

Whyte notation is generally used for steam locomotives throughout the United States, Canada, the United Kingdom and Ireland. For diesels and electrics, North America uses the AAR wheel arrangement scheme while British practice uses a slightly simplified form of the European UIC classification scheme (except for small diesel shunters, where Whyte notation is used).

In mainland Europe, the UIC classification scheme is generally used for all locomotive types including steam, with some exceptions. In France, the UIC classification is used for diesels and electrics while a scheme similar to the Whyte notation, but counting axles insteads of wheels, is used for steam locomotives. Notably, Switzerland had its own separate notation system until 1989, with the Swiss locomotive and railcar classification now only retained for its narrow gauge railways.

• AAR wheel arrangement - Used largely throughout the US and Canada for diesel and electric locomotives.
• UIC classification - Used in mainland Europe for all locomotive types. Used in the UK for electric and large diesel locomotives.
• Whyte notation - Used in North America, the UK and Ireland for steam locomotives, and for shunters (US: switchers) in the UK.