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 , it is widely used in North America to describe diesel and electric locomotives (including third-rail electric locomotives ). It is not used for steam locomotives , which use the Whyte notation instead (except geared steam locomotives , which are instead classified by their model and their number of trucks).
45-588: The EMD NW2 is a 1,000 hp (750 kW), B-B switcher locomotive manufactured by General Motors Electro-Motive Division of La Grange, Illinois . From February 1939 to December 1949, EMD produced 1,145 NW2s: 1,121 for U.S. and 24 for Canadian railroads. Starting in late 1948, the NW2s were manufactured in EMD's Plant #3 in Cleveland, Ohio. The locomotives were powered by a 12-cylinder model 567 engine and later
90-718: A hinge. Examples include the Milwaukee Road EF-1 "Boxcab" electrics. "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 uses narrow gauge GE "BB" locomotives with this arrangement, both with "standard" and wide cabs. A GE Dash 9-40BBW , for instance,
135-500: A mix of power cars and trailers, often with one of each in a pair which can be coupled to other pairs to form a larger train; see e.g. New Zealand FP class electric multiple unit . The power supply generation in Indian Railways is based on end-on-generation (EOG), in which a train's hotel load (power supply for lights, fans, air conditioning, pantry, etc.) is provided with electricity from 2 power cars attached to both ends of
180-457: A model 567A engine. In addition, EMD built three TR cow–calf paired sets, 36 TR2 cow–calf paired sets, and two TR3 cow–calf–calf sets. The TR sets were built before World War II ; the TR2 and TR3 sets afterward. Distinguishing features include two stacks in the middle of the hood, a half-height radiator grille, no sand box on the front platform, and no small louvers at the top front corners of
225-410: 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 (9.4 MW) (with four total prime-movers). With today's higher horsepower C-C units (about 4,300 hp (3.2 MW) apiece), three such C-C units exceeds the total power of
270-442: 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 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 . "1A-A1" means there are two trucks (or wheel assemblies) under
315-410: Is Brightline , which operates between Miami and Orlando International Airport . It is a trainset composed of two diesel bullet power cars at both ends and 4-7 passenger cars. Another traditional example would be the older InterCity 125 , made for and used by British Rail and several subsequent privatised bodies like Great Western Railway . Multiple units ( diesel or electric ) usually have
360-490: Is "Four axle". "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. Examples of this type were built as light rail vehicles. "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
405-408: Is "Six axle". "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 and FF2 electric locomotives used this arrangement. "2-C+C-2" means there are two sets of articulated axles under
450-523: 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" 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 -fired steam-turbine locomotives built by
495-584: Is a narrow-gauge adaptation of the SD45 , which required additional axles due to using smaller traction motors. "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 locomotives and
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#1732776148700540-751: 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. The Little Joes , Baldwin DR-12-8-1500/2 , and Baldwin 4-8+8-4-750/8-DE locomotives used this arrangement. "D-D" means there are two trucks each with four powered axles. Examples include the EMD DD units. D-D locomotives have fallen out of favor as nearly all of these were twin-engined locomotives, which placed too much horsepower in too few axles which made these consists rather inflexible (each locomotive featured two prime movers , making each unit essentially
585-399: Is a wide cab GE Dash 9-40CW series 4,000 hp (3,000 kW) locomotive with a B+B-B+B wheel arrangement. The EMD SD70ACe-BB produced from 2015 onward also has a B+B-B+B arrangement. "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
630-411: Is gradually being replaced by a newer energy-efficient power supply system called head-on generation (HOG), where power supply is drawn from overhead equipment through converters provided in electric locomotives for hotel load. This system is leading to huge savings in diesel fuel consumption (amounting to ₹ 1,182 crore (US$ 140 million) as on 20 November 2019). The NSW TrainLink XPT , which
675-551: Is under the back of the unit, and has one idler axle. Examples include the three EMD LWT12 locomotives built by EMD in 1956. Twenty SD70ACe-P4 locomotives were built by EMD with a B1-1B arrangement that has two three axle trucks with each truck having two AC traction motors and one idler axle nearest the fuel tank. The locomotive was designed as an AC traction alternative to the SD70M-2 that uses three DC traction motors on each of two three axle trucks. Only BNSF ordered
720-465: 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 Train-X equipment. "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
765-600: 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 1,000 hp (750 kW) cab unit, only one of which was built for the Chicago and North Western Railway in 1948. "A1A-A1A" means there are two trucks under the locomotive. Each truck has two powered axles, with an idler axle between them. This spreads
810-539: 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 800 hp (600 kW) railcar, six of which were built by the St. Louis Car Company exclusively for the Southern Railway in 1939. "A1-1A" means there are two trucks or wheel assemblies under
855-758: The Baldwin Locomotive Works for the Chesapeake and Ohio Railway between 1947 and 1948. This locomotive is sometimes called the M-1. "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 for Union Pacific . These locomotives consisted of two permanently coupled C-C units. "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
900-834: The British Rail Class 28 are the only locomotives to use this wheel arrangement. "C-C" means there are two identical trucks. Each truck has three powered axles. Examples include the EMD SD (Special Duty), GMD GF6C , EMD GM6C , PRR E44 , GE E60 , Virginian EL-C and GE Evolution Series 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 of "C-C"
945-931: The FM C-liners (most passenger units) built from 1950 to 1955, and the EMD FL9 . "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 , as well as switcher locomotives . Examples include the EMD GP (General Purpose), EMD F-units , EMD SW1500 , Acela Express Power Cars , Siemens Charger , Siemens ACS-64 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 of "B-B"
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#1732776148700990-621: The GE " Little Joe " electric locomotives . "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" means there are four sets of articulated axles under
1035-535: The Great Northern Z-1 electric locomotives (for the Cascade Tunnel electrification) used this arrangement. "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 electric locomotive used this arrangement. "2-D+D-2" means there are two sets of articulated axles under the unit. Within each of these sets, theare
1080-492: The Southern Railway in 1939. "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 streamliners. "3-A1A" means there are two trucks or wheel assemblies. The "3" truck
1125-546: The Texas Mexican Railway . "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 800 hp (600 kW) railcar, six of which were built by the St. Louis Car Company exclusively for
1170-584: The Virginian Railway 's EL-2B electric locomotives. Power car In rail transport , the expression power car may refer to either of two distinct types of rail vehicle: The first of these types of vehicle is closely related to the locomotive . What differentiates the locomotive and the first type of power car is their construction or use. A locomotive can be physically separated from its train and does nothing but provide propulsion and control (and heat or electricity for passenger trains). On
1215-459: 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
1260-505: The UK, the Class 31 uses this wheel arrangement. "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 . "B" means there are two powered axles under
1305-505: The center truck. The Russian VL85 and US-American EMD GM10B was a notable example. See also Bo-Bo-Bo . "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 GE boxcab electrics of 1923 are examples of this wheel arrangement. "2-B+B-2" means there are two sets of articulated axles under
1350-438: The center trucks. "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 locomotives made of three permanently coupled B-B units, which had solid drawbars connecting the units instead of the typical couplers. "C" means there are three powered axles under the unit. They are not articulated relative to other parts of
1395-509: The locomotive. This arrangement is only used on very small locomotives (e.g. the PRR B1 ). This arrangement is sometimes referred to as 0-6-0 , the Whyte notation equivalent. "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 , DE11 , and DE15 and
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1440-477: The model in 2014. The other locomotive with this wheel arrangement is the EMD SD70MACH , which is an SD70MAC rebuilt by Progress Rail for Metra and used for passenger service. In 2020, Metra approved of the purchase of 15 of these locomotives with options to purchase up to 27 more. "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
1485-741: The other hand, a power car of the first type is frequently an integral part of its train, and if the train uses distributed traction , some of the car's interior space may be used for carrying passengers or cargo. Nearly all high speed trains use power cars, frequently at both ends. An example of these are the Acela Express trainsets in use by Amtrak , which are built by Bombardier in Canada using technology licensed from France's Alstom. The twenty Acela trainsets operate between Washington, D.C. , and Boston, Massachusetts . Each trainset consists of six passenger cars and two power cars. Another example
1530-582: The sides of the hood. The predecessor of the NW2 was the NW1 . The "N" in NW1 stands for the nine in nine hundred hp (670 kW). The "W" in both models stands for "welded frame". AAR wheel arrangement#B-B The AAR system (like UIC) counts axles, unlike Whyte, which counts 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
1575-509: The span bolster. The Union Pacific 's M-10002 diesel streamliner and New York Central 's T-Motor 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" means there are four trucks. Each truck has two powered axles. The locomotive frame must allow for significant side play to be provided to
1620-427: The train. Each of these power cars is equipped with one diesel alternator set that supplies 3-phase power at 750 volts 50 Hz through two sets of feeders running along the rake and coupled in between with the help of inter-vehicle couplers. Each coach then picks up the power supply through a 60 kVA transformer and brings down the voltage to 110 volts, at which the equipment in compartments run. This technology
1665-462: 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 used this arrangement. "(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
1710-595: The unit. Each truck has one powered axle and one idler axle, with the idler axles to the outside. Examples include Budd RDC diesel multiple unit ( DMU ) cars. "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 in 1938, for greater stability at speed. "1-D" means there are two trucks or groups of axles;
1755-608: The unit. Each truck has one powered axle and one idler axle, with the powered axles to the outside. "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 . "A1A-3" means there are two trucks. The "A1A" truck
1800-466: 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 . It is also used on speeders . This arrangement is sometimes referred to as 0-4-0 , the Whyte notation equivalent. "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
1845-420: 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 's GG1 and Companhia Paulista 's electric locomotives were notable examples of this arrangement. "2+C-C+2" means there are two sets of axles under the unit. Within each of these sets, there
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1890-570: 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 and DD2 electric locomotives used this arrangement. "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
1935-499: The usual D-D consist by 300 hp (220 kW) (with one fewer prime-mover than a usual D-D consist, thereby significantly improving reliability and dramatically reducing maintenance). Although the D-D arrangement is associated with twin-prime-mover locomotives of high power, this does not mean a D-D with a single high-power prime mover may be built in the future, nor does it exclude two-truck, eight-axle electric locomotive. The EMD DDM45
1980-540: 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 and ALCO PAs , which were high speed passenger locomotives, and the dual service FM Erie-built . BNSF took delivery of ES44C4 locomotives with this type of truck in 2009. In
2025-679: Was used on the Jawn Henry coal -fired steam-turbine locomotive built by the Baldwin Locomotive Works for the Norfolk & Western Railway in May, 1954. "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 New York Central S-Motor third-rail electric locomotives (for the Grand Central Terminal electrification) and
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