Under the Whyte notation for the classification of steam locomotives by wheel arrangement, 2-4-0+0-4-2 is an articulated locomotive, usually of the Garratt type. The wheel arrangement is effectively two 2-4-0 locomotives operating back to back, with the boiler and cab suspended between the two power units. Each power unit has two leading wheels on one axle, four powered and coupled driving wheels on two axles and no trailing wheels. Since the 2-4-0 type is sometimes known as a Porter, the corresponding Garratt type would be referred to as a Double Porter. A similar wheel arrangement exists for Mallet locomotives, but is referred to as 2-4-4-2.