4-6-4+4-6-4

In the Whyte notation for the classification of steam locomotives by wheel arrangement, the 4-6-4+4-6-4 is a Garratt articulated locomotive. The wheel arrangement is effectively two 4-6-4 locomotives operating back to back, with the boiler and cab suspended between the two engine units. Each engine unit has two pairs of leading wheels in a leading bogie, followed by three coupled pairs of driving wheels, with two pairs of trailing wheels in a trailing bogie. Since the 4-6-4 type is sometimes known as a Baltic or Hudson, the corresponding Garratt type could be referred to as a Double Baltic or Double Hudson.