 Fairlies are most associated with the Ffestiniog Railway in Wales.While the Fairlie locomotives are 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.The Fairlie was invented and patented by the Scottish engineer Robert Francis Fairlie in 1864.