WHEEL ARRANGEMENT CLASSIFICATION
Here's a handy reference for you. Frederick Methvan Whyte's system of classification
is used to describe the wheel arrangement
of conventional steam locomotives. In this system, the first number is the number of leading wheels, and
the last is the number of trailing wheels. The middle number (or numbers) give the number and arrangement
of drivers. A "T" added at the end indicates a tank engine.
Note that some railroads had their own particular "type" name.
||4-wheel switcher, 4-coupled
||6-wheel switcher, 6-coupled
||8-wheel switcher, 8-coupled
||10-wheel switcher, 10-coupled
||Union (for Union RR, Pittsburgh)
||Columbia/Columbian (for New Zealand)
||Adriatic (quite rare, none in U.S.)
||Allegheny ("Blue Ridge" on the Virginian)
||Mikado (the "Mike"; called "MacArthur"s during WW2!)
||Berkshire (also called "Kanawha" on the C&O, "Lima" on the B&M)
||Angus, Mallet (Articulated)
||Mallet (Articulated), (Cab-Forward on SP, "Chesapeake" on the C&O)
||oOOOO OOOO OOOOo
||Triple Articulated, Triplex
||oOOOO OOOO OOOOoo
||Triple Articulated, Triplex (rear drivers under tender!)
||Santa Fe (known as "Decapod" on the S.P., "Central" on the IC)
||Texas ("Colorado" on the Burlington!, "Selkirk" on the C.P.)
||Mallet (Articulated), Virginian
||6-Wheeler, Jervis (Ca 1832!)
|4-2-2 or 4-2-4
||ooOo or ooOoo
||Bicycle (some uncertainty here!, more research needed!)
||American, or Eight-Wheeler
||Atlantic ("Chautauqua" by the Brooks Loco Works, "Milwaukee"
on, you guessed it, the Milwaukee Road!
||Reading (called "Jubilee" on the Central Pacific)
||4-cylinder Non-Articulated ("Duplex" on the Pennsy, "B&O" on B"O
||(two built for AT&SF)
||4-cylinder Non-Articulated, "Duplex-Drive" for the Pennsy
||Hudson ("Baltic" on the Milwaukee, "Shoreline" on the New Haven)
||Cab-Forward (S.P., 1911), 4-cylinder Articulated
||Challenger (U.P., 1936), 4-cylinder Articulated
||12-Wheeler, or "Mastodon" (C.P., 1882)
||Mountain ("Mohawk" on the NYC)
||Northern (also known by a bunch of other names! Confederation, Dixie, Golden State, etc.,etc.)
||Cab-Forward on S.P., 1928, Mallet (Articulated)
||Big Boy, Mallet (Articulated)
||Mastodon (C.P., 1883)
||Southern Pacific ("Overland" on U.P.)
||Crampton (Camden & Amboy, 1849)
||Pennsylvania (PRR, 1939)
Diesel wheel arrangements (in the U.S.A.) are classified by the AAR system. One powered
axle per truck is indicated by the letter "A", two powered axles by the letter "B",
three by the letter "C", and four by the letter "D". Non-powered, or "idler"
axles are indicated by numbers. I.e., A1A-A1A describes a locomotive with two trucks, each truck having a powered
axle, an idler axle, and another powered axle.
Examples (red indicates idler axles):
A1A-A1A (two trucks, each truck having a powered axle, an idler axle, and another powered axle)
B-B (two powered axles on each of two trucks)
C-C (three powered axles on each of two trucks)
I understand that about 90% of all U.S. diesel locomotive have one of the three
arrangements above. Don't confuse wheel arrangements with UNIT arrangements such as A-A, A-B, A-B-A.
Shay, Heisler, Climax and Willamette are various types of steam locomotives in which power was
transmitted to the drivers via a geared mechanism. The locomotives rode on two or three sets of trucks (four
trucks on some Shays). More on these later!
ELECTRICS, TURBINES, ETC.
I'm a-workin´ on it!