CLASSIFICATION OF LOCOMOTIVES
TYPE WHEEL ARRANGEMENT NAME O-4-O <OO 4 wheel switcher O-6-O <OOO 6 wheel swither 0-8-0 <OOOO 8 wheel switcher 0-10-0 <OOOOO 10 wheel switcher 0-10-2 <OOOOOo Union 2-4-2 <oOOo Columbia 2-6-0 <oOOO Mogul 2-6-2 <oOOOo Prairie 2-8-0 <oOOOO Consolidation 2-8-2 <oOOOOo Mikado 2-8-4 <oOOOOoo Berkshire 2-10-0 <oOOOOO Decapod 2-10-2 <oOOOOOo Santa Fe 2-10-4 <oOOOOOoo Texas 4-4-0 <ooOO American 4-4-2 <ooOOo Atlantic 4-4-4 <ooOOoo Jubilee 4-6-0 <ooOOO 10 Wheeler 4-6-2 <ooOOOo Pacific 4-6-4 <ooOOOoo Hudson 4-8-0 <ooOOOO 12 wheeler 4-8-2 <ooOOOOo Mountain 4-8-4 <ooOOOOoo Nothern 4-10-0 <ooOOOOO Mastodon 4-10-2 <ooOOOOOo Southern Pacific 4-12-2 <ooOOOOOOo Union Pacific 0-6-6-0 <OOO OOO Mallet Compound 2-6-6-0 <oOOO OOO Mallet Compound 2-6-6-2 <oOOO OOOo Mallet Compound 2-6-6-4 <oOOO OOOoo Simple Articulated 2-6-6-6 <oOOO OOOooo Allegheny 0-8-8-0 <OOOO OOOO Mallet Compound 2-8-8-0 <oOOOO OOOO Mallet Compound 2-8-8-2 <oOOOO OOOOo Simple Articulated 2-8-8-4 <oOOOO OOOOoo Yellowstone 2-8-8-8-2 <oOOOO OOOO OOOOo Triplex 2-8-8-8-4 <oOOOO OOOO OOOOoo Triplex 2-10-10-2 <oOOOOO OOOOOo Mallet Compound 4-4-4-4 <ooOO OOoo 4 cylinder non articulated 4-4-6-4 <ooOO OOOoo 4 cylinder non articulated 4-6-6-4 <ooOOO OOOoo Challenger 4-8-8-4 <ooOOOO OOOOoo Big Boy
STEAM LOCOMOTIVES are usually referred to by their classification in the Whyte system, developed by a New York Central official, which uses a series of numbers to show the number of pilot-truck wheels, drivers, and trailing truck wheels- for example, the early "American" type is a 4-4-0, which means that it has a four wheel pilot truck, two pairs of coupled drivers, and no trailing truck. Each group of drivers on articulated and multi-cylinder nonarticulated locomotives is shown separately- the Union Pacific's "Big Boy," the worlds biggest steam locomotive, is a 4-8-8-4. "Tank" locomotives, which have no separate tender but carry their water and fuel in tanks and bunkers on the locomotive itself, are designated by a "T" following the wheel arrangement; for example, 0-6-0T.
Electric and diesel locomotives are designated by the number of axles, non-powered axles are designated by numbers, powered axles by letters. The small locomotives used on many electric lines, diesel switchers, and many diesel freight units are "B-B," indicating that they have two four wheel power trucks; many diesel passenger units are "A1A-A1A," since they have two 6-wheel trucks with only the first and third axles powered. "C-C" would indicate a six wheel truck with all three axles powered. "D-D" indicated an eight wheel truck with all four axles powered.
While the above chart does not show all of the locomotive types that were used, it covers the common types of steam locomotives found in the United States.
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