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 20th century. Whyte's system counts the number of leading wheels, then the number of driving wheels, and finally the number of trailing wheels, this being the common pattern of the conventional steam locomotive. Thus, a locomotive with two leading axles (and thus four wheels) in front, then three driving axles (six wheels) and followed by one trailing axle (two wheels) is classified as a 4-6-2. It's important to stress that wheels, not axles, are what is counted in this system. Other classification schemes in use elsewhere (such as in France) count axles. The system had to be extended with the advent of articulated locomotives. The scheme generally adopted is that locomotives such as Garratts, where there are, in effect, two separate locomotives joined by a common boiler, are classified by using a plus sign in between the arrangements of each engine. Thus, a 'double Pacific' type Garratt is a 4-6-2+2-6-4. Simpler articulated types such as Mallets, where there are no unpowered axles in between powered axles, are just written by adding extra numbers in the middle; each number represents a grouping of wheels. Thus a Big Boy is written under this modified Whyte notation as a 4-8-8-4; there are two leading axles, one group of four driving axles, another group of four driving axles, and then two trailing axles. In addition the suffix 'T' is often used to indicate a tank locomotive (otherwise, a tender locomotive is assumed). In British practice, this is sometimes extended to indicate what type of tank locomotive. When this is done, a plain 'T' means side tank, 'ST' means saddle tank, PT means pannier tank and WT stands for well tank. Where a 'T' suffix is followed by '+T', this indicates a tank locomotive that has a tender for additional coal or water capacity. The limitations of the Whyte system for classifying locomotives that did not fit the standard steam locomotive pattern led to the design of other forms of classification. Most commonly used in Europe is the UIC classification scheme, based on German practice, which can more completely define the exact layout of a locomotive. In American (and to a lesser extent British) practice, most wheel arrangements in common use were given names. Here is a list of the most common wheel arrangements: in the illustration, which should be read left to right, with the front of the locomotive to the left, small o is a carrying axle, and a big O is a driving axle.

align=left\|Arrangement!!align=left\|Whyte Classification!!align=left\|Name
olspan="3"\|Non-Articulated Locomotives
o	0-2-2
O	2-2-0	Planet
Oo	2-2-2	Single, Jenny Lind
Ooo	2-2-4
oO	4-2-0	Jervis
oOo	4-2-2	Bicycle
oOoo	4-2-4
ooO	6-2-0	Crampton
O	0-4-0	Four-Coupled
Oo	0-4-2
Ooo	0-4-4
OO	2-4-0	Porter
OOo	2-4-2	Columbia
OOoo	2-4-4
oOO	4-4-0	American, Eight-wheeler
oOOo	4-4-2	Atlantic
oOOoo	4-4-4	Reading, Jubilee (Canada)
OO	0-6-0	Six-Coupled
OOo	0-6-2
OOoo	0-6-4
OOO	2-6-0	Mogul
OOOo	2-6-2	Prairie
OOOoo	2-6-4	Adriatic
oOOO	4-6-0	Ten-Wheeler (not Britain)
oOOOo	4-6-2	Pacific
oOOOoo	4-6-4	Hudson, Baltic
OOO	0-8-0	Eight-Coupled
OOOo	0-8-2
OOOO	2-8-0	Consolidation
OOOOo	2-8-2	Mikado, Mike, MacArthur
OOOOoo	2-8-4	Berkshire, Kanawha
oOOOO	4-8-0	Mastodon
oOOOOo	4-8-2	Mountain, Mohawk
oOOOOoo	4-8-4	Northern, Niagara, Confederation, Dixie, Greenbrier, Pocono, Potomac
ooOOOOooo	6-8-6	(Used only by the Pennsylvania Railroad's steam turbine locomotive)
OOOO	0-10-0	Ten-Coupled, (rarely) Decapod
OOOOo	0-10-2	Union
OOOOO	2-10-0	Decapod
OOOOOo	2-10-2	Santa Fe
OOOOOoo	2-10-4	Texas, Selkirk (Canada)
oOOOOO	4-10-0	Mastodon, Gobernador
oOOOOOo	4-10-2	Southern Pacific, Overland
OOOOO	0-12-0	Twelve-Coupled
OOOOOO	2-12-0	Centipede
OOOOOOo	2-12-2
OOOOOOoo	2-12-4
oOOOOOOo	4-12-2	Union Pacific
oOOOOOOOoo	4-14-4	(Only one engine ever used this arrangement, the Soviet AA20. It was a failure.)
olspan="3"\|Duplex Locomotives
oOO OOoo	4-4-4-4	Duplex
ooOO OOooo	6-4-4-6	Pennsylvania
oOO OOOoo	4-4-6-4	(PRR Q2)
oOOO OOoo	4-6-4-4	(PRR Q1)
olspan="3"\|Mallet and Simple Articulated Locomotives
O-OO	0-4-4-0
-OO-OO-o	2-4-4-2
OO-OOO	0-6-6-0	Erie
OOO-OOO	2-6-6-0	Denver & Salt Lake
OOO-OOOo	2-6-6-2
OOO-OOOoo	2-6-6-4	Norfolk & Western
OOO-OOOooo	2-6-6-6	Allegheny
oOOO-OOOoo	4-6-6-4	Challenger
OOO-OOOO	0-8-8-0	Angus
OOOO-OOOO	2-8-8-0	Bull Moose
OOOO-OOOOo	2-8-8-2	Chesapeake
OOOO-OOOOoo	2-8-8-4	Yellowstone (and, running in reverse, SP Cab Forward)
oOOOO-OOOOo	4-8-8-2	(Southern Pacific cab forward)
oOOOO-OOOOoo	4-8-8-4	Big Boy
OOOOO-OOOOOo	2-10-10-2	(Santa Fe and Virginian RR's)
OOOO-OOOO-OOOO-o	2-8-8-8-2	Triplex (Erie RR)
OOOO-OOOO-OOOO-oo	2-8-8-8-4	Triplex

Garratts are almost always two identical locomotive frames back-to-back, and are thus called Double Pacifics, Double Northerns etc.

Whyte Notation

See also