0-4-4-0

In the Whyte notation for the classification of steam locomotive wheel arrangement, an 0-4-4-0 is a locomotive with no leading wheels, two sets of four driving wheels, and no trailing wheels. The arrangement is chosen to give the articulation of a locomotive with only the short rigid wheelbase of an 0-4-0, but with its weight spread across eight wheels, and with all the weight carried on the driving wheels; effectively a flexible 0-8-0. Articulated examples were constructed as Mallet, Meyer, BMAG and Double Fairlie locomotives and also as geared locomotives such as Shay, Heisler, and Climax types.^[1] A similar configuration was used on some Garratt locomotives, but it is referred to as 0-4-0+0-4-0. In the electric and diesel eras, the Bo-Bo is comparable and closest to the Meyer arrangement of two swivelling bogies.^{[citation needed]}

Although rigid duplex locomotives were also constructed with pairs of driving axles and the 0-4-4-0 driven arrangement, these were intended for express passenger service and so were given 4-4-4-4 overall arrangements with leading and trailing bogies for stability.^{[citation needed]}

A few Mallet locomotives were built as 0-4-4-0 tender locomotives, mostly by Baldwin for narrow gauge lines, but all others were 0-4-4-0T tank locomotives. As one of the main goals of this arrangement was to place the most adhesion weight on the drivers, it was sensible to include the weight of coal and water with this.