usually means a steam locomotive
with one or more engine units which can move independent of the main frame. This is done to allow a longer locomotive to negotiate tighter curves. Articulated locomotives are generally used either on lines with extreme curvature—logging, industrial, or mountainous railways, for example—or to allow very large locomotives to run on railways with standard track curvature.
Articulated locomotives saw service in many nations, but were very popular on narrow gauge railways
in Europe and saw their greatest size developed in the United States, where the Union Pacific Big Boy 4-8-8-4s
and the Allegheny H-8 2-6-6-6s
were some of the largest steam locomotives ever built.
Many different schemes for articulation were developed over the years. Of these, the Mallet locomotive
and its simple-expansion derivative were the most popular, followed by the Garratt
type (mostly built in the United Kingdom
, popular throughout Europe
and European colonies), and the various geared steam locomotive
types, the latter largely used in logging, mining and industry. Most other types saw only limited success.
Steam locomotive types
These are the major types of articulated locomotive; there were large numbers of other designs.
- The Fairlie, with two powered trucks under a double boiler, or its Single Fairlie single-boiler derivative with one powered and one unpowered truck (known as a Mason Bogie in the United......