A 6-4-4-6 steam locomotive, in the

Whyte notation Whyte notation is a classification method for steam locomotives, and some internal combustion locomotives and electric locomotives, by wheel arrangement. It was devised by Frederick Methvan Whyte, and came into use in the early twentieth cen ...

for describing locomotive

wheel arrangement In rail transport, a wheel arrangement or wheel configuration is a system of classifying the way in which wheels are distributed under a locomotive. Several notations exist to describe the wheel assemblies of a locomotive by type, position, and c ...

s, is one with six

leading wheel The leading wheel or leading axle or pilot wheel 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 on a leading truck. Leading wheels are used ...

s, two sets of four driving wheels, and six

trailing wheel On a steam locomotive, a trailing wheel or trailing axle is generally an unpowered wheel or axle ( wheelset) located behind the driving wheels. The axle of the trailing wheels is usually located in a trailing truck. On some large locomotives, ...

s. Other equivalent classifications are: * UIC classification: 3BB3 (also known as German classification and

Italian classification The UIC classification of locomotive axle arrangements, sometimes known as the German classification''The Railway Data File''. Leicester: Silverdale, 2000. p. 52. . or German system,Kalla-Bishop P.M. & Greggio, Luciano, ''Steam Locomotives'', Cre ...

) *

French classification Under the French classification system for locomotive wheel arrangements, the system is slightly different for steam and electric/diesel vehicles. Steam The French system counts axles, rather than wheels. As with Whyte notation, a conventional r ...

: 3223 *

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. Thus 0-6-0 beco ...

: 2525 *

Swiss classification For more than a century, the Swiss locomotive, multiple unit, motor coach and railcar classification system, in either its original or updated forms, has been used to name and classify the rolling stock operated on the railways of Switzerland. ...

: 2/5+2/5 up to the early 1920s, later 4/10 Only one was produced, the Pennsylvania Railroad's sole class S1 of 1939. It was a

duplex locomotive A duplex locomotive is a steam locomotive that divides the driving force on its wheels by using two pairs of cylinders rigidly mounted to a single locomotive frame; it is not an articulated locomotive. The concept was first used in France in 1 ...

, the longest and heaviest rigid frame reciprocating steam locomotive ever built and is referred to as the ''Pennsylvania Type''. This experimental locomotive was exhibited at the 1939 New York World's Fair, and was afterward placed in limited service between

Chicago, Illinois (''City in a Garden''); I Will , image_map = , map_caption = Interactive Map of Chicago , coordinates = , coordinates_footnotes = , subdivision_type = Country , subdivision_name ...

, and

Crestline, Ohio Crestline is a village in Crawford and Richland Counties in the U.S. state of Ohio. Crestline's population was 4,630 at the 2010 census. It is the third largest municipality in Crawford County. The Crawford County portion of Crestline is part ...

. The locomotive was too large to work elsewhere in the system. Pennsylvania Railroad executive hopes that the locomotive could haul 1,000 tons at 100 miles per hour were realized in a December 1940 test run which reached 101 mph with 1350 tons behind the locomotive. It was capable of very high speeds. However no firm documentary evidence has so far surfaced to confirm speeds such as the 133 mph run cited in the December 1941 issue of Popular Mechanics magazine which, if true, would make this locomotive the fastest steam locomotive in world history.

References

* Loco Profile 24: Pennsylvania Duplexii by Brian Reed (June 1972) * Pennsy Power (I) by Alvin F. Staufer (1962) * "High-Capacity Locomotive for Fast Service" Railway Age Vol. 106, No. 25 (24 June 1939) * "Riding the Gargantua of the Rails" by Roderick M. Grant, Popular Mechanics (December 1941) * http://www.steamlocomotive.com/locobase.php?country=USA&wheel=Duplex&railroad=prr * http://www.crestlineprr.com/duplexexperimentals.html * http://www.dieselpunks.org/profiles/blogs/sunday-streamline-14-the-big * http://streamlinermemories.info/?p=5258 {{Whyte types 44,6-4-4-6 cs:Lokomotiva S 1-6.100