page_title: 4-8-4
section_title: Development
hierarchical_section_title: 4-8-4 / Overview / Development
caption_attribution_description: Čeština: Union Pacific 844 v Painted Rocks, Nevada, na cestě z Elko do Sparks, Nevada, 15. září 2009. Deutsch: Union Pacific 844 in Painted Rocks, Nevada, auf der Fahrt von Elko nach Sparks, Nevada, 15. April 2009. English: Union Pacific 844 at Painted Rocks, Nevada, on a run from Elko to Sparks, Nevada, April 15, 2009. Italiano: Union Pacific 844 a Painted Rocks, Nevada, sul percorso da Elko a Sparks, Nevada, 15 aprile 2009. ქართული: ორთქლმავალი Union Pacific 844 საექსკურსიო შემადგენლობით მიემართება ელკოდან - სპარკსში, ნევადა, აშშ (2009 წელი). Македонски: Локомотива Union Pacific 844 кај Пејнтед Рокс (Невада) на пат од Елко до Спаркс. Nederlands: De Union Pacific 844 bij Painted Rocks in de Amerikaanse staat Nevada, onderweg van Elko naar Sparks op 15 september 2009. Slovenčina: Union Pacific 844 v Painted Rocks, Nevada, na ceste z Elko do Sparks, Nevada, 15. september 2009. 中文（简体）‎: 联合太平洋铁路844蒸汽机车，2009年9月15日从美国内华达州埃尔科驶往斯巴克斯。
context_page_description: Under the Whyte notation for the classification of steam locomotives, 4-8-4 represents the wheel arrangement of four leading wheels on two axles, eight powered and coupled driving wheels on four axles and four trailing wheels on two axles. The type was first used by the Northern Pacific Railway, and initially named the Northern Pacific, but railfans and railroad employees have shortened the name when referring to the type, and now is most commonly known as a Northern.
context_section_description: The 4-8-4 wheel arrangement was a progression from the 4-8-2 Mountain type and, like the 2-8-4 Berkshire and 4-6-4 Hudson types, an example of the "Super Power" concept in steam locomotive design that made use of the larger firebox that could be supported by a four-wheel trailing truck, which allowed greater production of steam. The four-wheel leading truck gave stability at speed and the eight driving wheels gave greater adhesion.  The evolution to the 4-8-4 type occurred in the United States of America soon after the Lima Locomotive Works introduced the concept of "Lima Super Power" in 1925, making heavy 2-8-2 and 2-8-4 locomotives. The prototype was built by American Locomotive Company (ALCO) for the Northern Pacific Railway (NP) in 1926, with a very large firebox with a 100-square-foot (9.3 m²) grate, designed to burn low quality lignite coal. The four-wheel trailing truck weighed about 15,000 pounds (6.8 t) more than two-wheel trucks of the time and could carry an additional 55,000 pounds (25 t) of engine weight; the difference of 40,000 pounds (18 t) was available for increased boiler capacity.
  The 4-8-4 type arrived when nearly all the important steam locomotive design improvements had already been proven, including Superheaters, mechanical stokers, outside valve gear and the Delta trailing truck. One-piece, cast steel bed-frames with integrally cast cylinders gave the strength and rigidity to use Roller bearings. In 1930, the Timken Company used the Timken 1111, a 4-8-4 built by ALCO with roller bearings on all axles, to demonstrate the value of their sealed roller bearings. The Timken 1111 was subsequently sold to the NP, where it became NP No. 2626, their sole Class A-1 locomotive.
  The stability of the 4-8-4 wheel arrangement meant that driving wheels up to 80 inches (2.0 m) diameter could be used for high speed passenger and fast freight operation. Lateral control devices allowed these locomotives to traverse relatively sharp curves despite their eight-coupled drivers. The increased boiler size possible with this type, together with the high axle loads permitted on mainlines in North America, resulted in the design of some massive locomotives, some of which weighed more than 350 tons with tender included. The 4-8-4 was suitable for both express passenger and fast freight service, though it was not suited to heavy drag freight trains.
  Although locomotives of the 4-8-4 wheel arrangement were used in a number of countries, those that were developed outside North America included various design features which set them apart from North American practice. Scaled down examples of the type were exported by two American builders, ALCO and Baldwin Locomotive Works, for 1,000 mm (3 ft 3 ³⁄₈ in) metre gauge lines in Brazil. Most were two-cylinder locomotives, but five classes of three-cylinder 4-8-4s were built:
  The simplex 06 class by the Deutsche Reichsbahn in Germany.
  The simplex H class by the Victorian Railways in Australia.
  The compound 242A1 class of the Société nationale des chemins de fer français (SNCF) in France.
  The simplex 477 class tank engines by CKD for Czechoslovak State Railways; 60 4-8-4T locomotives were built between 1951 and 1955, the last new steam engines built in Czechoslovakia.
  An experimental high-pressure compound locomotive of the New York Central (NYC).
caption: Union Pacific 844, the only steam locomotive never retired by a North American Class I railroad.
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