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). Most double-ended Fairlies had wheel arrangements of 0-4-4-0T or 0-6-6-0T.

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.