4-6-6-4 - AbsoluteAstronomy.com

Whyte notation

The Whyte notation for classifying steam locomotives by wheel arrangement was devised by Frederick Methvan Whyte and came into use in the early twentieth century encouraged by an editorial in American Engineer and Railroad Journal...

, a 4-6-6-4 is a railroad steam locomotive

Steam locomotive

A steam locomotive is a railway locomotive that produces its power through a steam engine. These locomotives are fueled by burning some combustible material, usually coal, wood or oil, to produce steam in a boiler, which drives the steam engine...

that has four leading wheel

Leading wheel

The leading wheel or leading axle of a steam locomotive is an unpowered wheel or axle located in front of the driving wheels. The axle or axles of the leading wheels are normally located in a truck...

s followed by six coupled driving wheel

Driving wheel

On a steam locomotive, a driving wheel is a powered wheel which is driven by the locomotive's pistons...

s, a second set of six driving wheels and four trailing wheel

Trailing wheel

On a steam locomotive, a trailing wheel or trailing axle is generally an unpowered wheel or axle located behind the driving wheels. The axle of the trailing wheels was usually located on a trailing truck...

s.

Other equivalent classifications are:

UIC classification

UIC classification

The UIC classification of locomotive axle arrangements describes the wheel arrangement of locomotives, multiple units and trams. It is set out in the International Union of Railways "Leaflet 650 - Standard designation of axle arrangement on locomotives and multiple-unit sets". It is used in much...

: 2CC2 (also known as German classification and Italian classification)

French classification: 230+032

Turkish classification

Turkish classification

In the Turkish classification system for railway locomotives, the number of powered axles are followed by the total number of axles. It is identical to the Swiss system except that the latter places a slash between the two numbers.Thus0-6-0 becomes 33...

: 35+35

Swiss classification: 3/5+3/5

The UIC classification

UIC classification

is refined to (2'C)C2' for Mallet locomotives.

This wheel arrangement

Wheel arrangement

In rail transport, a wheel arrangement is a system of classifying the way in which wheels are distributed beneath a locomotive.. Several notations exist to describe the wheel assemblies of a locomotive by type, position, and connections, with the adopted notations varying by country...

was used by the Challenger
Union Pacific Challenger
Built between 1936 and 1943, the Challengers were nearly 122 feet long and weighed more than one million pounds. Articulated like their big brother, the Union Pacific Big Boy, the Challengers had a 4-6-6-4 wheel arrangement...

class of locomotives on the Union Pacific Railroad

Union Pacific Railroad

The Union Pacific Railroad , headquartered in Omaha, Nebraska, is the largest railroad network in the United States. James R. Young is president, CEO and Chairman....

. One locomotive of this class, Union Pacific 3985

Union Pacific 3985

Union Pacific 3985 or UP 3985 is a four-cylinder simple articulated 4-6-6-4 Challenger-type steam locomotive owned by Union Pacific Railroad. The UP 3985 locomotive was built in 1943 by the American Locomotive Company of Schenectady, New York...

is still operable, and it is currently the largest operable steam locomotive in the world. Another example, Union Pacific 3977

Union Pacific 3977

Union Pacific 3977 or UP 3977 is a 4-6-6-4 steam locomotive originally owned by Union Pacific Railroad. Its counterpart, Union Pacific 3985, is the largest operating steam locomotive in the world. 3977 was donated to the City of North Platte, Nebraska for display on October 19, 1968...

is on static display in North Platte, Nebraska

North Platte, Nebraska

North Platte is a city in and the county seat of Lincoln County, Nebraska, United States. It is located in the southwestern part of the state, along Interstate 80, at the confluence of the North and South Platte Rivers forming the Platte River...

.

Though originally intended for freight service, many units could be found leading passenger consists as well. Railroads that used the Challenger type locomotive include:

4-6-6-4 construction roster
Railroad (quantity)	Class	Road numbers	Builder	Build year	Notes
Clinchfield Railroad Clinchfield Railroad The Clinchfield Railroad was an operating and holding company for the Carolina, Clinchfield and Ohio Railway . The line ran from the coalfields of Virginia and Elkhorn City, Kentucky, to the textile mills of South Carolina... (12 new, 6 secondhand)	E-1	650–657	ALCO American Locomotive Company The American Locomotive Company, often shortened to ALCO or Alco , was a builder of railroad locomotives in the United States.-Early history:...	1942–1943
	E-2	660–663	ALCO American Locomotive Company The American Locomotive Company, often shortened to ALCO or Alco , was a builder of railroad locomotives in the United States.-Early history:...	1947
	E-3	670–675	ALCO American Locomotive Company The American Locomotive Company, often shortened to ALCO or Alco , was a builder of railroad locomotives in the United States.-Early history:...	1943	ex-D&RGW Denver and Rio Grande Western Railroad The Denver & Rio Grande Western Railroad , often shortened to Rio Grande or D&RGW, formerly the Denver & Rio Grande Railroad, is a defunct U.S. railroad company. The railroad started as a narrow gauge line running south from Denver, Colorado in 1870; however, served mainly as a transcontinental... , acquired 1947
Delaware and Hudson Railway Delaware and Hudson Railway The Delaware and Hudson Railway is a railroad that operates in the northeastern United States. Since 1991 it has been a subsidiary of the Canadian Pacific Railway, although CPR has assumed all operations and the D&H does not maintain any locomotives or rolling stock.It was formerly an important... (40)	J	1500–1539	ALCO	1940–1946
Denver and Rio Grande Western Railroad Denver and Rio Grande Western Railroad The Denver & Rio Grande Western Railroad , often shortened to Rio Grande or D&RGW, formerly the Denver & Rio Grande Railroad, is a defunct U.S. railroad company. The railroad started as a narrow gauge line running south from Denver, Colorado in 1870; however, served mainly as a transcontinental... (21)	L-105	3700–3709	Baldwin Baldwin Locomotive Works The Baldwin Locomotive Works was an American builder of railroad locomotives. It was located in Philadelphia, Pennsylvania, originally, and later in nearby Eddystone, Pennsylvania. Although the company was very successful as a producer of steam locomotives, its transition to the production of...	1938
	L-105	3710–3714	Baldwin	1942
	L-97	3800–3805	ALCO	1943	to Clinchfield Railroad in 1947
Great Northern Railway (2 secondhand)	Z-6	4000–4001	ALCO	1937	ex-SP&S Spokane, Portland and Seattle Railway The Spokane, Portland and Seattle Railway was a United States-based railroad incorporated in 1905. It was a joint venture by the Great Northern Railway and the Northern Pacific Railway to build a railroad along the north bank of the Columbia River.... 903–904; sold back to SP&S March 1950 and July 1946 respectively
Northern Pacific Railway Northern Pacific Railway The Northern Pacific Railway was a railway that operated in the west along the Canadian border of the United States. Construction began in 1870 and the main line opened all the way from the Great Lakes to the Pacific when former president Ulysses S. Grant drove in the final "golden spike" in... (47)	Z-6	5100–5120	ALCO	1936–1937
	Z-7	5121–5126	ALCO	1941
	Z-8	5130–5149	ALCO	1943–1944
Spokane, Portland and Seattle Railway Spokane, Portland and Seattle Railway The Spokane, Portland and Seattle Railway was a United States-based railroad incorporated in 1905. It was a joint venture by the Great Northern Railway and the Northern Pacific Railway to build a railroad along the north bank of the Columbia River.... (8)	Z-6	900–905	ALCO	1937	Identical to NP Z-6 class; 903–904 sold to GN January 1940; purchased back March 1950 and July 1946 respectively
	Z-8	910–911	ALCO	1944	Identical to NP Z-8 class
Union Pacific Railroad Union Pacific Railroad The Union Pacific Railroad , headquartered in Omaha, Nebraska, is the largest railroad network in the United States. James R. Young is president, CEO and Chairman.... (105)	CSA-1	3900–3914	ALCO	1936	to UP 3800–3814
	CSA-2	3915–3939	ALCO	1937	to UP 3815–3839
	4664-3	3950–3969	ALCO	1942
	4664-4	3975–3999	ALCO	1943
	4664-5	3930–3949	ALCO	1944
Western Maryland Railway Western Maryland Railway The Western Maryland Railway was an American Class I railroad which operated in Maryland, West Virginia, and Pennsylvania. It was primarily a coal hauling and freight railroad, with a small passenger train operation. The WM became part of the Chessie System in 1973 and ceased operating its lines... (12)	M-2	1201–1212	Baldwin	1940–1941	These and the 15 units for the D&RGW were the only ones of this type made by Baldwin.
Western Pacific Railroad Western Pacific Railroad The Western Pacific Railroad was a Class I railroad in the United States. It was formed in 1903 as an attempt to break the near-monopoly the Southern Pacific Railroad had on rail service into northern California... (7)	M-100	401–407	ALCO	1938

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