Editing 2-8-8-4 (section)

{{Short description|Articulated locomotive wheel arrangement}}
{{More footnotes|date=May 2010}}
[[Image:Duluth Missabe and Iron Range 2-8-8-4 locomotive.jpg|thumb|Duluth, Missabe & Iron Range 2-8-8-4 "Yellowstone" No. 229, as preserved in 1987]]
A '''2-8-8-4''' steam locomotive, under the [[Whyte notation]], has two [[leading wheel]]s, two sets of eight [[driving wheel]]s, and a four-wheel [[trailing truck]]. The type was generally named the ''Yellowstone'', a name given it by the first owner, the [[Northern Pacific Railway]], whose lines ran near [[Yellowstone National Park]]. Seventy-two Yellowstone-type locomotives were built for four U.S. railroads.

Other equivalent classifications are:
*[[UIC classification]]: '''1DD2''' (also known as [[UIC classification of locomotive axle arrangements|German classification]] and [[Italian classification]])
*[[French classification]]: '''140+042'''
*[[Turkish classification]]: '''45+46'''
*[[Swiss classification]]: '''4/5+4/6'''
*[[:ru:Осевая формула паровоза#Русский|Russian classification]]: '''1-4-0+0-4-2'''

The equivalent UIC classification is, refined for simple articulated locomotives, '''(1′D)D2′'''.

A locomotive of this length must be an [[articulated locomotive]]. All Yellowstones had fairly small drivers of {{Convert|63|to|64|in|m|sigfig=3}}. (For greater speeds, the [[Union Pacific Railroad]] chose a four-wheel leading truck and drivers of {{Convert|68|in|m|sigfig=3}} for its [[Union Pacific Big Boy|Big Boy]] 4-8-8-4 class.)

Several classes of Yellowstone, especially the [[Duluth, Missabe and Iron Range]]'s locomotives, are among the largest steam locomotives, with the exact ranking depending on the criteria used.