4-8-4+4-8-4

NSWGR AD60 Garratt no. 6012 tops the grade at Cowan

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

Overview

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).^[1]

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.^[1]

One of the East African Railways locomotives survives, number 87 of 1940 in the Nairobi Railway Museum. Four of the New South Wales AD60 class have been preserved^[2]

References

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