4-8-8-4

Common card · No. 420352

A 4-8-8-4, in the Whyte notation for the classification of steam locomotives by wheel arrangement, is a locomotive with a four-wheel leading truck, two sets of eight driving wheels, and a four-wheel trailing truck. Only one model of locomotives has ever used this wheel configuration, and that is commonly known as "Union Pacific Big Boys" after the railroad that operated them. Other equivalent classifications are: UIC classification: '2DD2' (also known as German classification and Italian classification) French locomotive classification: '240+042' Turkish locomotive classification: '46+46' Swiss classification: '4/6+4/6' Russian classification: 2-4-4-2 or 2-4-0+0-4-2 The equivalent UIC classification is refined to (2′D)D2′ for simple articulated locomotives. A similar wheel arrangement exists for Garratt locomotives, but is referred to as 4-8-0+0-8-4 since both engine units swivel. 4-8-8-4 Big Boys were only produced for the Union Pacific Railroad. Twenty-five such engines were built between...

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