The AAR wheel arrangement system is a method of classifying locomotive (or unit) wheel arrangements that was developed by the Association of American Railroads. Essentially a simplification of the European

UIC 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 ...

, it is widely used in

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...

to describe

diesel Diesel may refer to: * Diesel engine, an internal combustion engine where ignition is caused by compression * Diesel fuel, a liquid fuel used in diesel engines * Diesel locomotive, a railway locomotive in which the prime mover is a diesel engin ...

and

electric locomotive An electric locomotive is a locomotive powered by electricity from overhead lines, a third rail or on-board energy storage such as a battery or a supercapacitor. Locomotives with on-board fuelled prime movers, such as diesel engines or gas ...

s (including third-rail electric locomotives). It is not used for

steam locomotive A steam locomotive is a locomotive that provides the force to move itself and other vehicles by means of the expansion of steam. It is fuelled by burning combustible material (usually coal, oil or, rarely, wood) to heat water in the locomot ...

s, which use the Whyte notation instead. The AAR system counts axles instead of wheels. Letters refer to powered axles, and numbers to unpowered (or idler) axles. "A" refers to one powered axle, "B" to two powered axles in a row, "C" to three powered axles in a row, and "D" to four powered axles in a row. "1" refers to one idler axle, and "2" to two idler axles in a row. A dash ("–") separates

trucks A truck or lorry is a motor vehicle designed to transport cargo, carry specialized payloads, or perform other utilitarian work. Trucks vary greatly in size, power, and configuration, but the vast majority feature body-on-frame construction ...

or wheel assemblies. A plus sign ("+") refers to articulation, either by connecting bogies with span bolsters or by connecting individual locomotives via solid drawbars instead of

couplers Coupler may refer to: Engineering Mechanical * Railway coupler, a mechanism for connecting rolling stock in a train device ** Janney coupler ** SA3 coupler ** Scharfenberg coupler for multiple unit passenger cars * Quick coupler, used in constru ...

1A-A1

"1A-A1" means there are two trucks (or wheel assemblies) under the unit. Each truck has one powered axle and one idler axle, with the idler axles to the outside. Examples include Budd RDC Diesel MU ( DMU) cars.

1B-1B

"1B-1B" means there are two trucks with a leading idler axle in front of two powered axles. This arrangement was used to upgrade the B-B arrangement of two EMC 1800 hp B-B locomotives owned by the

Santa Fe Railroad The Atchison, Topeka and Santa Fe Railway , often referred to as the Santa Fe or AT&SF, was one of the larger railroads in the United States. The railroad was chartered in February 1859 to serve the cities of Atchison and Topeka, Kansas, and S ...

in 1938, for greater stability at speed.

1-D

"1-D" means there are two trucks or groups of axles; the "1" truck is under the front of the unit, and has one idler axle. The remaining 4 axles are rigidly mounted to the frame behind this lead truck (or grouped in a second truck). This is roughly the equivalent of a 2-8-0 Consolidation in the Whyte notation, particularly when built as a 1-truck/4 rigid axle locomotive. The only known examples are a series of diesel boxcab locomotives built and owned by the Texas Mexican Railway.Texas-Mexican 701A
/ref>

2-A1A

"2-A1A" means there are two trucks or wheel assemblies. The "2" truck is under the front of the unit, and has two idler axles in a row. The "A1A" truck is under the rear of the unit, and has one powered axle, one idler axle, and one more powered axle. An example is the FM OP800 railcar, six of which were built by the St. Louis Car Company exclusively for the Southern Railway in 1939.

2-B

"2-B" means there are two trucks or wheel assemblies. The "2" truck is under the front of the unit, and has two idler axles in a row. The "B" truck is under the rear of the unit, and has two powered axles. Examples include the three lightweight power cars built by ALCO/ ACF in 1935 and 1937 for use with the

Rebel A rebel is a participant in a rebellion. Rebel or rebels may also refer to: People * Rebel (given name) * Rebel (surname) * Patriot (American Revolution), during the American Revolution * American Southerners, as a form of self-identification; s ...

streamliners.

3-A1A

"3-A1A" means there are two trucks or wheel assemblies. The "3" truck is under the front of the unit, and has three idler axles in a row. The "A1A" truck is under the rear of the unit, and has one powered axle, one idler axle, and one more powered axle. An example is the later built FM OP800 railcar, six of which were built by the St. Louis Car Company exclusively for the Southern Railway in 1939.

A1-1A

"A1-1A" means there are two trucks or wheel assemblies under the unit. Each truck has one powered axle and one idler axle, with the powered axles to the outside.

A1A-2

"A1A-2" means there are two trucks. The "A1A" truck is under the front of the unit, and has one powered axle, one idler axle, and one more powered axle. The "2" truck is under the back of the unit, and has two idler axles in a row. An example is the ''Silver Charger'' power car for the

General Pershing Zephyr The ''General Pershing Zephyr'' was the ninth of the Chicago, Burlington & Quincy Railroad's ''Zephyr'' streamliners, and the last built as an integrated streamliner rather than a train hauled by an EMD E-unit diesel locomotive. It was constr ...

A1A-3

"A1A-3" means there are two trucks. The "A1A" truck is under the front of the unit, and has one powered axle, one idler axle, and one more powered axle. The "3" truck is under the back of the unit, and has three idler axles in a row. An example is the

Baldwin DR-6-2-10 Baldwin Locomotive Works produced several different Baldwin DR-6 models of 6-axle passenger train-hauling diesel locomotives between 1945 and 1948. The series comprised eight individual versions, all of which sold only in small numbers; across al ...

cab unit, only one of which was built for the

Chicago and North Western Railway The Chicago and North Western was a Class I railroad in the Midwestern United States. It was also known as the "North Western". The railroad operated more than of track at the turn of the 20th century, and over of track in seven states befor ...

in 1948.

A1A-A1A

"A1A-A1A" means there are two trucks under the locomotive. Each truck has two powered axles, with an idler axle between them. This spreads the weight of the locomotive more evenly over the track and counteracts the tendency of trucks to oscillate at high speeds, which is a problem with two axle trucks. The idler wheels may be smaller than the powered wheels. Examples of locomotives with this wheel arrangement include the

EMD E-units EMD E-units were a line of passenger train streamliner diesel locomotives built by the General Motors Electro-Motive Division (EMD) and its predecessor the Electro-Motive Corporation (EMC). Final assembly for all E-units was in La Grange, Illino ...

and

ALCO PA The ALCO PA was a family of A1A-A1A diesel locomotives built to haul passenger trains. The locomotives were built in Schenectady, New York, in the United States, by a partnership of the American Locomotive Company (ALCO) and General Electric ...

s, which were high speed passenger locomotives, and the dual service

FM Erie-built The Erie-built was the first streamlined, cab-equipped dual service diesel locomotive built by Fairbanks-Morse, introduced as direct competition to such models as the ALCO PA and FA and EMD FT. F-M lacked the space and staff to design and manufa ...

. BNSF took delivery of

ES44C4 The Evolution Series is a line of diesel locomotives built by GE Transportation Systems (now owned by Wabtec), initially designed to meet the U.S. EPA's Tier 2 locomotive emissions standards that took effect in 2005. The first pre-production ...

locomotives with this type of truck in 2009. In the UK, the Class 31 uses this wheel arrangement.

A1A-B+B

"A1A-B+B" means there are three trucks. The first truck has three axles, with the center one unpowered. A pair of two-axle trucks, each with both axles powered, are connected by a span bolster under the rear of the unit. The only example to date of this arrangement was a single experimental

EMD SDP45 The SDP45 is a six-axle, C-C, diesel-electric locomotive built by General Motors' Electro-Motive Division of La Grange, Illinois. It was a passenger-hauling version of the SD45 on a stretched locomotive frame with an extended, squared-off long ...

B

"B" means there are two powered axles under the unit. These axles are not articulated relative to other parts of the locomotive. This arrangement is only used on very small locomotives, such as the

EMD Model 40 The EMD Model 40 was a two-axle diesel-electric locomotive built by Electro-Motive Corporation (EMC), and its corporate successor, General Motors' Electro-Motive Division (EMD) between August 1940 and April 1943. Nicknamed ''"critters"'', eleven ...

. This arrangement is sometimes referred to as

0-4-0 Under the Whyte notation for the classification of steam locomotives, represents one of the simplest possible types, that with two axles and four coupled wheels, all of which are driven. The wheels on the earliest four-coupled locomotives were ...

, the Whyte notation equivalent.

B-1

"B-1" means there are two trucks. The "B" truck is under the front of the unit, and has two powered axles. The "1" truck is under the back of the unit, and has one idler axle. Examples include the three

EMD LWT12 The EMD LWT12 was a diesel–electric power car that was built in 1955 by General Motors Electro-Motive Division (EMD), to pull a lightweight passenger trainset. The General Motors Company developed both components under the project name, ''T ...

locomotives built by EMD in 1956.

B-2

"B-2" means there are two trucks. The "B" truck is under the front of the unit, and has two powered axles. The "2" truck is under the back of the unit, and has two idler axles in a row. Examples include the three lightweight RP-210 locomotives built by Baldwin in 1956 and 1957 for use with

Pullman-Standard The Pullman Company, founded by George Pullman, was a manufacturer of railroad cars in the mid-to-late 19th century through the first half of the 20th century, during the boom of railroads in the United States. Through rapid late-19th century ...

Train-X equipment.

B-A1A

"B-A1A" means there are two trucks. The "B" truck is under the front of the unit, and has two powered axles. The "A1A" truck is under the back of the unit, and has one powered axle, one idler axle, and one more powered axle. Examples include some of the FM C-liners (most passenger units) built from 1950 to 1955, and the EMD FL9.

B-B

"B-B" means there are two identical trucks. Each truck has two powered axles, a currently popular configuration used in high-speed, low-weight applications such as intermodal trains and

high-speed rail High-speed rail (HSR) is a type of rail system that runs significantly faster than traditional rail, using an integrated system of specialised rolling stock and dedicated tracks. While there is no single standard that applies worldwide, lines ...

, as well as in switching. Examples include the EMD GP (General Purpose),

EMD F-units EMD F-units are a line of diesel-electric locomotives produced between November 1939 and November 1960 by General Motors Electro-Motive Division and General Motors-Diesel Division. Final assembly for all F-units was at the GM-EMD plant at La Gra ...

, EMD SW1500, ''Acela Express'' Power Cars,

Siemens Charger The Siemens Charger is a family of diesel-electric passenger locomotives designed and manufactured by Siemens Mobility for the North American market. There are five variants of the Charger, tailored for different operators and types of service ...

Siemens ACS-64 The Siemens ACS-64, or Amtrak Cities Sprinter, is an electric locomotive designed by Siemens Mobility for use on the Northeast Corridor (NEC) and the Keystone Corridor in the northeastern United States. The design was based on locomotives Sieme ...

and GE Genesis units. High speed ("time") freight trains, with guaranteed schedules often use B-B locomotives of 3,800 HP (950 HP per axle), but this application, too, has largely been replaced by higher-powered, 4,500 HP C-C locomotives (750 HP per axle). An American

Colloquialism Colloquialism (), also called colloquial language, everyday language or general parlance, is the style (sociolinguistics), linguistic style used for casual (informal) communication. It is the most common functional style of speech, the idiom norm ...

of "B-B" is "Four axle".

B-2-B

"B-2-B" means there are three trucks. The center truck has two unpowered axles and the truck at each end has two powered axles. The locomotive frame must either articulate or allow for significant side play to be provided to the center truck.

B-B-B

"B-B-B" means there are three trucks. Each truck has two powered axles. The locomotive frame must either articulate or allow for significant side play to be provided to the center truck. The Russian

VL 85 VL and variants may refer to: *Daisy V/L, the first production rifle for caseless ammunition *Holden VL Commodore, an automobile introduced by Holden in 1986 *Air Via (IATA airline designator VL) *Valtion Lentokonetehtaat, the Finnish State aircraft ...

and US-American

EMD GM10B The GM10B was a solitary electric testbed locomotive with a power output of which was intended for use on high-speed freight services on the Northeast Corridor. Built by American locomotive builder Electro-Motive Division (EMD) at its La Grange, ...

was a notable example. See also

Bo-Bo-Bo A Bo-Bo-Bo or Bo′Bo′Bo′ (UIC classification) is a locomotive with three independent two-axle bogies with all axles powered by separate traction motors. In the AAR system, this is simplified to B-B-B. The Bo-Bo-Bo configuration is of ...

B+B+B

"B+B+B" means there are three articulated sets of two powered axles each under the unit. The locomotive frame must allow for significant side play to be provided to the center axle set, as well as allowing for end play for the end sets. The ten

Mexican Railway The Mexican Railway (''Ferrocarril Mexicano'') was one of the primary pre-nationalization railways of Mexico. Incorporated in London in September 1864 as the Imperial Mexican Railway (''Ferrocarril Imperial Mexicano'') to complete an earlier p ...

GE boxcab electrics of 1923 are examples of this wheel arrangement.

2-B+B-2

"2-B+B-2" means there are two sets of articulated axles under the unit. Within each of these sets, there is a truck with two idler axles, and inboard of it are two powered axles. Two of these articulated sets are placed back to back and connected by a hinge. The

PRR DD1 The Pennsylvania Railroad DD1 was a class of boxcab electric locomotives built by the Pennsylvania Railroad. The locomotives were developed as part of the railroad's New York Tunnel Extension, which built the original Pennsylvania Station in New ...

and DD2

s used this arrangement.

2-B+B+B+B-2

"2-B+B+B+B-2" means there are two sets of articulated axles under the unit. Within each of these sets, there is a truck with two idler axles, and inboard of it are two powered axles, hinged to yet another set of two powered axles. Two of these articulated sets are placed back to back and connected by a hinge. Examples include the Milwaukee Road EF-1 "Boxcab" electrics.

B+B-B+B

"B+B-B+B" means there are four trucks under the unit. Within each truck, there are two powered axles, and pairs of them are connected by span bolsters. One example would be the General Electric U50, built from 1963 to 1965. The 4500 horsepower (3.4 MW) turbine locomotives built by GE for Union Pacific also used this arrangement. The EFVM railway of

Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...

uses narrow gauge GE "BB" locomotives with this arrangement, both with "standard" and wide cabs. A GE Dash 9-40BBW, for instance, is a wide cab GE Dash 9-40CW series locomotive with a B+B-B+B wheel arrangement.

B-B+B-B

"B-B+B-B" means that the locomotive has four trucks. Each truck contains two powered axles. The middle pair of trucks are connected by a span bolster. In most cases, the locomotive is articulated over the span bolster. The Union Pacific's M-10002 diesel streamliner and

New York Central The New York Central Railroad was a railroad primarily operating in the Great Lakes and Mid-Atlantic regions of the United States. The railroad primarily connected greater New York and Boston in the east with Chicago and St. Louis in the Midw ...

T-Motor T-Motor was the class designation given by the New York Central to its ALCO- GE built T-1a, T-1b, T-2a, T-2b, and T-3a electric locomotives. The T-Motors were the New York Central's second electric locomotive purchase after the original class of ...

third rail electric locomotives are examples of this type. This arrangement also includes locomotives made of two permanently coupled B-B units, such as some EMD FT units which had a solid drawbar connecting two units instead of the typical couplers.

B-B-B-B

"B-B-B-B" means there are four trucks. Each truck has two powered axles. The locomotive frame must allow for significant side play to be provided to the center trucks.

B-B+B-B+B-B

"B-B+B-B+B-B" means that the locomotive has six trucks. Each truck contains two powered axles. The only known locomotives to have this configuration were the two

EMD TR3 EMD may refer to: Finance and commerce * Emerging market debt * Earnest money deposit, in the United States, a security deposit, especially for real estate Medicine * Electromagnetic diaphragm * Electromechanical dissociation * Emergency me ...

locomotives made of three permanently coupled B-B units, which had solid drawbars connecting the units instead of the typical couplers.

C

"C" means there are three powered axles under the unit. They are not articulated relative to other parts of the locomotive. This arrangement is only used on very small locomotives (e.g. the

PRR B1 The Pennsylvania Railroad's class B1 comprised 42 switcher-type electric locomotives built between 1926 and 1935. They were of 0-6-0 wheel arrangement in the Whyte notation with 700 horsepower. As built, the first 28 locomotives in the 1926 or ...

). This arrangement is sometimes referred to as

0-6-0 Under the Whyte notation for the classification of steam locomotives, represents the wheel arrangement of no leading wheels, six powered and coupled driving wheels on three axles and no trailing wheels. This was the most common wheel arrangemen ...

, the Whyte notation equivalent.

C-B

"C-B" means there are two trucks. The "C" truck is under the front of the unit, and has three powered axles. The "B" truck is under the rear of the unit, and has two powered axles. The Japanese

DE10 The is a class of Japanese C-B wheel arrangement diesel-hydraulic locomotives. 708 locomotives were built between 1966 and 1978. , 138 locomotives remained in operation. Variants DE10-0 subclass 158 DE10-0 locomotives were built with steam h ...

and DE11 locomotives use this wheel arrangement.

C-C

"C-C" means there are two identical trucks. Each truck has three powered axles. Examples include the EMD SD (Special Duty),

GMD GF6C The GF6C was an electric locomotive for freight duties built by General Motors Diesel in collaboration with ASEA of Sweden. Seven of these locomotives were built in 1983 and 1984, for use on the BC Rail's electrified Tumbler Ridge subdivision. ...

EMD GM6C The GM6C was a solitary testbed electric locomotive for freight duties built by General Motors' Electro-Motive Division of the United States in collaboration with ASEA of Sweden. It was rolled out from EMD's La Grange, Illinois plant on May 1 ...

PRR E44 The PRR E44 was an electric, rectifier-equipped locomotive built by General Electric for the Pennsylvania Railroad between 1960 and 1963. The PRR used them for freight service on the Northeast Corridor. They continued in service under Penn Centr ...

, GE E60, Virginian EL-C and

GE Evolution Series The Evolution Series is a line of diesel locomotives built by GE Transportation Systems (now owned by Wabtec), initially designed to meet the U.S. EPA's Tier 2 locomotive emissions standards that took effect in 2005. The first pre-production u ...

units, except the ES44C4 and ET44C4 which use the A1A-A1A wheel arrangement. This is a currently popular configuration used in low-speed, high-weight applications, such as unit coal trains. General ("manifest") freight trains also use C-C locomotives. See also Co-Co. An American

colloquialism Colloquialism (), also called colloquial language, everyday language or general parlance, is the style (sociolinguistics), linguistic style used for casual (informal) communication. It is the most common functional style of speech, the idiom norm ...

of "C-C" is "Six axle".

1-C+C-1

"1-C+C-1" means there are two sets of articulated axles under the unit. Within each of these sets, there is a truck with one idler axle, and inboard of it are three powered axles. Two of these articulated sets are placed back to back and connected by a hinge. The

PRR FF1 The Pennsylvania Railroad's class FF1 was an American electric locomotive, a prototype numbered #3931 and nicknamed "Big Liz". It was built in 1917 to haul freight trains across the Allegheny Mountains where the PRR planned to electrify. "Big ...

and FF2 electric locomotives used this arrangement.

2-C+C-2

"2-C+C-2" means there are two sets of articulated axles under the unit. Within each of these sets, there is a truck with two idler axles, and inboard of it are three powered axles. Two of these articulated sets are placed back to back and connected by a hinge. The

Pennsylvania Railroad The Pennsylvania Railroad (reporting mark PRR), legal name The Pennsylvania Railroad Company also known as the "Pennsy", was an American Class I railroad that was established in 1846 and headquartered in Philadelphia, Pennsylvania. It was named ...

GG1 The Pennsylvania Railroad GG1 is a class of streamlined electric locomotives built for the Pennsylvania Railroad (PRR), in the northeastern United States. The class was known for its striking art deco shell, its ability to pull trains at up to 10 ...

electric locomotives were notable examples of this arrangement.

2+C-C+2

"2+C-C+2" means there are two sets of axles under the unit. Within each of these sets, there is a guiding truck with two idler axles, and inboard of this, and hinged to it, is a truck with three powered axles. The GE steam turbine-electric locomotives of 1939 were notable examples of this arrangement.

2-C1+2-C1-B

"2-C1+2-C1-B" means there are five trucks. Only the first three axles on the four-axle trucks were powered, as were both axles in the last truck; the first and middle trucks had two unpowered axles each. The only examples of this arrangement were three unique

coal Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal is formed when dea ...

-fired

steam-turbine locomotive A steam turbine locomotive is a steam locomotive which transmits steam power to the wheels via a steam turbine. Numerous attempts at this type of locomotive were made, mostly without success. In the 1930s this type of locomotive was seen as a way ...

s built by the

Baldwin Locomotive Works The Baldwin Locomotive Works (BLW) was an American manufacturer of railroad locomotives from 1825 to 1951. Originally located in Philadelphia, it moved to nearby Eddystone, Pennsylvania, in the early 20th century. The company was for decades t ...

for the

Chesapeake and Ohio Railway The Chesapeake and Ohio Railway was a Class I railroad formed in 1869 in Virginia from several smaller Virginia railroads begun in the 19th century. Led by industrialist Collis P. Huntington, it reached from Virginia's capital city of Richmond t ...

between 1947 and 1948. This locomotive is sometimes called the M-1.

C-C+C-C

"C-C+C-C" means there are four trucks under the unit. Each truck has three powered axles. The only examples of this type were the 8500 horsepower (6.3 MW) turbine locomotives built by

General Electric General Electric Company (GE) is an American multinational conglomerate founded in 1892, and incorporated in New York state and headquartered in Boston. The company operated in sectors including healthcare, aviation, power, renewable energ ...

for Union Pacific. These locomotives consisted of two permanently coupled C-C units.

C+C-C+C

"C+C-C+C" means there are four trucks. Each truck has three powered axles and pairs of them are connected by span bolsters. This arrangement was used on the '' Jawn Henry''

-fired

built by the

for the Norfolk & Western Railway in May, 1954.

1-D-1

"1-D-1" means there are three trucks under the unit. At either end are trucks with one idler axle; the center truck has four powered axles. The original 1904–1909

S-Motor S-Motor was the class designation given by the New York Central to its ALCO- GE built S-1, S-2, S-2a and S-3 electric locomotives. The S-Motors hold the distinction of being the world's first mass-produced main line electric locomotives with the ...

third-rail electric locomotives (for the

Grand Central Terminal Grand Central Terminal (GCT; also referred to as Grand Central Station or simply as Grand Central) is a commuter rail terminal located at 42nd Street and Park Avenue in Midtown Manhattan, New York City. Grand Central is the southern terminus ...

electrification) and the

Great Northern Z-1 The Great Northern Z-1 was a class of ten electric locomotives built for the Great Northern Railway They were used to work the route through the second Cascade Tunnel. They were built between 1926–1928 by Baldwin Locomotive Works, with Westing ...

electric locomotives (for the Cascade Tunnel electrification) used this arrangement.

2-D-2

"2-D-2" means there are three trucks. At either end are trucks with two idler axles; the center truck has four powered axles. The

PRR R1 PRR may refer to: * Parietal reach region, of the human brain * Pattern recognition receptor, receptors of the innate immune system that identify pathogen-associated molecular patterns * Pennsylvania Railroad (reporting mark), an American railroad ...

electric locomotive used this arrangement.

D-D

"D-D" means there are two trucks. Each truck has four powered axles. Examples include the EMD DD units. D-D locomotives so far have fallen out of favor as nearly all of these have been twin-engined locomotives, which placed too much horsepower in too few axles, thereby making these consists rather inflexible (each locomotive featured two prime movers, making each unit essentially a pair of high-powered B-B locomotives on a common frame as far as traction and power was concerned). In fact, a usual consist of a D-D unit included a leading C-C unit and a trailing C-C unit, for a total of about 12,600 HP (with four total prime-movers). With today's higher horsepower C-C units (about 4,300 HP apiece), three such C-C units exceeds the total power of the usual D-D consist by 300 HP (with one fewer prime-mover than a usual D-D consist, thereby significantly improving reliability and dramatically reducing maintenance). Although at this time the term D-D is associated with twin-prime-mover locomotives of high power, this does not preclude the possibility of a D-D with a single prime mover of high power some time in the future, nor of the term being used to describe a two-truck, eight-axle electric locomotive. The

EMD DDM45 The EMD DDM45 is a Metre-gauge railway, meter-gauge Diesel-electric transmission, diesel-electric locomotive built by Electro-Motive Diesel, EMD. The DD in the name means that it has eight axles in two trucks, giving it a AAR wheel arrangement#D- ...

is a narrow-gauge adaptation of the

SD45 The SD45 is a six-axle diesel-electric locomotive built by General Motors Electro-Motive Division between 1965 and 1971. It has an EMD 645E3 twenty-cylinder engine generating on the same frame as the SD38, SD39, SD40, and SDP40. As of 2022, mos ...

, which required additional axles due to the use of smaller traction motors.

2-D+D-2

"2-D+D-2" means there are two sets of articulated axles under the unit. Within each of these sets, there is a truck with two idler axles, and inboard of it are four powered axles. Two of these articulated sets are placed back to back and connected by a hinge. Examples include the Baldwin DR-12-8-1500/2 "Centipede"

diesel locomotive A diesel locomotive is a type of railway locomotive in which the prime mover is a diesel engine. Several types of diesel locomotives have been developed, differing mainly in the means by which mechanical power is conveyed to the driving whee ...

s and the GE " Little Joe"

B-D+D-B

"B-D+D-B" means there are two sets of articulated axles under the unit. Within each of these sets, there is a truck with two powered axles, and inboard of it are four powered axles. Two of these articulated sets are placed back to back and connected by a hinge. The W-1 class of electric locomotives built by General Electric for the Great Northern Railway used this arrangement.

1B+D+D+B1

"1B+D+D+B1" means there are four sets of articulated axles under the unit. At each end, there is one unpowered axle and two powered axles, hinged to a set of four powered axles. Two of these articulated sets are placed back to back and connected by a hinge. The "Bi-Polar" electric locomotives used by the

Milwaukee Road The Chicago, Milwaukee, St. Paul and Pacific Railroad (CMStP&P), often referred to as the "Milwaukee Road" , was a Class I railroad that operated in the Midwestern United States, Midwest and Pacific Northwest, Northwest of the United States fr ...

used this arrangement.

(B+B-B+B)+(B+B-B+B)

"(B+B-B+B)+(B+B-B+B)" means there are 2 units, each with 4 trucks in a B+B-B+B wheel arrangement. An example was the

Virginian Railway The Virginian Railway was a Class I railroad located in Virginia and West Virginia in the United States. The VGN was created to transport high quality "smokeless" bituminous coal from southern West Virginia to port at Hampton Roads. History ...

's EL-2B electric locomotives.

References

{{DEFAULTSORT:Aar Wheel Arrangement Locomotive classification systems