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.

The Whyte notation is a classification method for steam locomotives, and some internal combustion locomotives and electric locomotives, by wheel arrangement. It was devised by Frederick Methvan Whyte, and came into use in the early twentieth century following a December 1900 editorial in American Engineer and Railroad Journal.