Under the Whyte notation for the classification of steam locomotives by wheel arrangement, a 4-8-2+2-8-4 is a Garratt articulated locomotive consisting of a pair of 4-8-2 engine units back to back, with the boiler and cab suspended between them. The 4-8-2 wheel arrangement has four leading wheels on two axles, usually in a leading bogie, eight powered and coupled driving wheels on four axles and two trailing wheels on one axle, usually in a trailing truck. Since the 4-8-2 type is generally known as a Mountain, the corresponding Garratt type is usually known as a Double Mountain.