Fairlie locomotive

A Fairlie locomotive is a type of articulated steam locomotive that has the driving wheels on bogies. The locomotive may be double-ended (a double Fairlie) or single ended (a single Fairlie).

While the Fairlie locomotives are now used only on heritage railways, the vast majority of diesel and electric locomotives in the world today follow a form not very different from the Fairlie — two power trucks with all axles driven, and many also follow the Fairlie's double-ended concept, capable of being driven equally well in both directions.