4-6-6-4

In Whyte notation, a 4-6-6-4 is a railroad steam locomotive that has four leading wheels followed by six coupled driving wheels, a second set of six driving wheels and four trailing wheels.

Other equivalent classifications are:

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

French classification: 230+032

Turkish classification: 35+35

Swiss classification: 3/5+3/5

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

This wheel arrangement was used by the "Challenger" class of locomotives on the Union Pacific Railroad. One locomotive of this class, Union Pacific 3985 is still operable, and it is currently the largest operable steam locomotive in the world. Another example, Union Pacific 3977 is on static display in North Platte, Nebraska.

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

External links

* [http://www.steamlocomotive.com/challenger The Challenger Type Locomotive]
* [http://www.northeast.railfan.net/challenger.html The Union Pacific Challenger Roster]
* [http://www.toytrains1.com/challenger.htm Web Site of ToyTrains1 4-6-6-4 Challenger Steam Locomotives]