Wheel arrangement

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 instead 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.

Geared steam locomotives such as Shays, Heislers, and Climaxes do not have a standard wheel arrangement classification system.