Editing 4-8-8-4

{{Short description|Articulated locomotive wheel arrangement}}
[[File:UP 4014 Cruising.jpg|thumb|right|300px|A [[Union Pacific Big Boy|Big Boy locomotive]]. This example is [[Union Pacific 4014]].]]
[[File:WheelArrangement 4-8-8-4.svg|thumb|300px|right|4-8-8-4 wheel arrangement]]
A '''4-8-8-4''' in the [[Whyte notation]] for the classification of [[steam locomotive]]s by [[wheel arrangement]], is a locomotive with a four-wheel [[leading truck]], two sets of eight [[driving wheel]]s, and a four-wheel [[trailing truck]]. Only one model of locomotives has ever used this wheel configuration, and that is commonly known as "[[Union Pacific Big Boy]]s" after the railroad that operated them.<ref>{{cite web| url=http://www.steamlocomotive.com/bigboy/| title=Union Pacific Big Boys| work=SteamLocomotive.com| access-date=2008-02-08| url-status=dead| archive-url=https://web.archive.org/web/20090922043838/http://www.steamlocomotive.com/bigboy/| archive-date=22 September 2009}}</ref>

Other equivalent classifications are:
* [[UIC classification of locomotive axle arrangements|UIC classification]]: '2DD2' (also known as German classification and Italian classification)
* [[French locomotive classification]]: '240+042'
* [[Turkish locomotive classification]]: '46+46'
* [[Swiss classification]]: '4/6+4/6'

The equivalent UIC classification is refined to (2′D)D2′ for simple [[articulated locomotive]]s.

A similar wheel arrangement exists for [[Garratt locomotive]]s, but is referred to as {{whyte|4-8-0+0-8-4}} since both engine units swivel.

4-8-8-4 Big Boys were only produced for the [[Union Pacific Railroad]]. Twenty-five such engines were built between 1941 and 1944, numbered 4000 to 4024. Eight of these locomotives survive, seven of which are on static public display at various sites in the [[United States]]. Union Pacific announced plans in August 2013<ref>{{cite web |url=https://www.up.com/aboutup/community/community_ties/0815_4014.htm |title=UP: Big Wheels Not Yet Turnin' |author= Union Pacific Community Ties |access-date=9 December 2017}}</ref> to restore [[Union Pacific 4014|No. 4014]] to operation for use in mainline excursion service. No. 4014 underwent restoration between 2016 and 2019, and completed its first post-restoration test run on May 2, 2019.<ref>{{cite web |url=http://trn.trains.com/Home/Union%20Pacific%20Big%20Boy/Landing%20Page/2013/08/Union%20Pacific%20Big%20Boys.aspx |title=Union Pacific Big Boy: Rebirth of a Legend |author=Trains Magazine |access-date=22 October 2013}}</ref><ref>{{cite web |url=https://www.up.com/aboutup/community/inside_track/america-celebrates-transcontinental-railroad-5-1-19.htm |title=America Celebrates the Transcontinental Railroad |author=Union Pacific Community Ties |access-date=3 May 2019}}</ref>

The UP Big Boys were an expansion of the {{whyte|4-6-6-4}} "Challenger" type articulated locomotive. Adding four driving wheels increased the pulling power of the locomotive and reduced the need for helper locomotives over steep grades. Although their wheels were an inch (25.4&nbsp;mm) smaller than those of the Challengers, they were still able to sustain similar high speeds.

Other American railroads considered buying 4-8-8-4s, including the [[Western Pacific Railroad]], which already rostered large 2-8-8-2s and 4-6-6-4s, but [[diesel locomotive]]s were gaining popularity and soon were able to displace these Big Boy locomotives.

==References==
{{reflist}}

==External links==
*[https://web.archive.org/web/20090922043838/http://www.steamlocomotive.com/bigboy/ www.steamlocomotive.com]
*[http://www.toytrains1.com/bigboy.htm Web Site of ToyTrains1 4-8-8-4 Big Boy Steam Locomotives]

{{Whyte types}}

[[Category:4-8-8-4 locomotives| ]]
[[Category:Whyte notation|88,4-8-8-4]]


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