In the Whyte notation for the classification of steam locomotives by wheel arrangement, the 4-8-4+4-8-4 is a Garratt articulated locomotive. The wheel arrangement is effectively two 4-8-4 locomotives operating back to back, with the boiler and cab suspended between the two engine units. Each engine unit has a two pairs of leading wheels in a leading bogie, followed by four coupled pairs of driving wheels, with two pairs of trailing wheels in a trailing bogie. Since the 4-8-4 type is sometimes known as a Northern, the corresponding Garratt type could be referred to as a Double Northern.
Other equivalent classifications are:
- UIC classification: 2D2+2D2 (also known as German and Italian classifications)
- French classification: 242+242
- Turkish classification: 48+48
- Swiss classification: 4/8+4/8 up to the early 1920s, later 8/16
There were only two classes of 4-8-4+4-8-4 steam locomotives across the globe, all of which were constructed by Beyer, Peacock. The first to be built were thirty class EC3 for the 1,000 mm (3 ft 3 3⁄8 in) metre gauge Kenya Uganda Railway (KUR), constructed in three batches in 1939, 1940 and 1949. These later became classes 57 and 58 on the East African Railways (EAR).
The second were the AD60 class Garratts of the Australian 4 ft 8 1⁄2 in (1,435 mm) standard gauge New South Wales Government Railways, of which forty-seven were constructed in 1952. The last five of these were delivered in pieces, as spare parts. Forty three 60 class were assembled, the last entering service in 1956 and the last withdrawn from service in 1973. 
One of the East African Railways locomotives survives, no. 87 of 1940 in the Nairobi Railway Museum.
Four of the New South Wales AD60 class have been preserved. 6039 and 6042 are owned by Dorrigo Steam Railway and Museum Ltd. The N.S.W. 60 class weigh 260 imperial tons and are the largest locomotives in the Southern Hemisphere. 
|1,000 mm||Kenya Uganda Railway||EC3||6905-6910||6||1939||Beyer, Peacock|
|1,000 mm||Kenya Uganda Railway||EC3||6970-6975||6||1940||Beyer, Peacock|
|1,000 mm||Kenya Uganda Railway||EC3||7290-7307||18||1949||Beyer, Peacock|
|4 ft 8 1⁄2 in||New South Wales Government Railways||AD60||7473-7497||25||1952||Beyer, Peacock|
|4 ft 8 1⁄2 in||New South Wales Government Railways||AD60||7528-7544||17||1952||Beyer, Peacock|
|4 ft 8 1⁄2 in||New South Wales Government Railways||AD60 in pieces as spares||7545-7549||5||1952||Beyer, Peacock|
- Hamilton, Gavin N., The Garratt Locomotive - Garratt Locomotives produced by Beyer, Peacock, retrieved 10 November 2012
- Hamilton, Gavin N., The Garratt Locomotive - Surviving Garratt Locomotives, retrieved 10 November 2012.
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