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).
51-527: The ALCO FA is a family of B-B diesel locomotives designed to haul freight trains . The locomotives were built by a partnership of ALCO and General Electric in Schenectady, New York , between January 1946 and May 1959. Designed by General Electric's Ray Patten (along with their ALCO PA cousins), they were of a cab unit design; both cab-equipped lead ( A unit ) FA and cabless booster ( B unit ) FB models were built. A dual passenger-freight version,
102-700: 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,
153-410: 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
204-442: 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
255-490: 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
306-408: 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
357-523: 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
408-570: 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
459-740: 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
510-399: 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
561-546: 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
SECTION 10
#1732858941738612-465: 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
663-587: 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
714-528: 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
765-739: 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
816-813: 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"
867-916: 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"
918-508: The FPA-2/FPB-2 variants) was built between October 1950 and June 1956. Finally, the 1,800 hp (1,300 kW) FPA-4/FPB-4 , powered by the 251 V-12 engine, was built between October 1958 and May 1959 by ALCO's Canadian subsidiary, Montreal Locomotive Works (MLW). The FAs, as well as their cousins, the ALCO PAs , were born as a result of ALCO's development of a new diesel engine design,
969-756: The FPA/FPB , was also offered. It was equipped with a steam generator for heating passenger cars . ALCO's designation of F marks these locomotives as being geared primarily for freight use, whereas the P designation of the PA sets indicates that they were geared for higher speeds and passenger use. However, beyond this their design was largely similar - aside from the PA/PB's both being larger A1A-A1A types with an even more striking nose - and many railroads used FA and PA locomotives for both freight and passenger service. Several examples of FAs and FBs have been preserved. While most are now in
1020-608: 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
1071-520: 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
SECTION 20
#17328589417381122-712: The South Australian Railways (SAR) in 1955 as the 930 class . In 1957, the SAR received the first of an eventual 31 built to a two-cab design, the end with the second cab being flat-fronted. A few months later, the first of an up-rated version of the two-cab design arrived on the Department of Railways New South Wales as the 44 class , of which 100 were in service by 1968. Number Numbers Similar DL500 locomotives were also used in Greece, Pakistan, Peru, and Spain. In India
1173-488: 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
1224-532: 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
1275-455: 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
1326-572: The Americas where ALCO-built cab units, such as All America Latina Logistica (ALL), still see daily usage in freight duty is Argentina. A total of 369 DL500 locomotives were built by ALCO, AE Goodwin , and MLW between May 1953 and December 1967. Variants of the ALCO "World Locomotive" saw service in Australia, where it was built under license by AE Goodwin , Sydney . Six single-cab locomotives were delivered to
1377-743: The Baltimore and Ohio and the Erie. By this time, however, the cab unit had fallen out of favor due to the greater versatility of road switchers, and US production of the FA line ended in 1956, with Canadian production ending in 1959. From the 1970s until 1999, the Long Island Rail Road used 20 FA units converted into "power packs". The traction motors were removed, and original prime movers replaced with 600 horsepower (450 kW) engines/generators solely for supplying Head-end power (HEP). The engineer's control stand
1428-633: The DL500 were introduced as the Indian locomotive class WDM-1 in 1957. They were in service until the early 2000s. Number 12. Craig, R. (2010, December 29). Alco DL500 World Locomotives . www.the diesel shop.us. Retrieved April 5, 2023, from http://thedieselshop.us/Alco_DL500.HTML 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
1479-455: The Model 244. In early 1944, development started on the new design, and by November 1945, the first engines were beginning to undergo tests. This unusually short testing sequence was brought about by the decision of ALCO's senior management that the engine and an associated line of road locomotives had to be introduced no later than the end of 1946. In preparation for this deadline, by January 1946,
1530-498: 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
1581-680: The care of railroad museums, a few remain in operational status on such lines as the Cuyahoga Valley Scenic Railroad , Grand Canyon Railway and the Napa Valley Wine Train . Three different models were offered. The FA-1/FB-1 , which featured a 1,500 horsepower (1,100 kW) rating, was built from January 1946 to October 1950, with a 1,600 hp (1,200 kW) version produced between March and August 1950 (many early models were subsequently upgraded to 1,600 hp). The 1,600 hp (1,200 kW) FA-2/FB-2 (along with
ALCO FA - Misplaced Pages Continue
1632-505: 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
1683-438: 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
1734-629: The equivalent of an FPA-2 riding on A1A trucks. ALCO's "World Locomotive", the DL500 (introduced in 1953), originated as a newly designed demonstrator based on the FA-2. The first 25 DL500s used the model 244 engine rated at 1,600 horsepower (1,200 kW). Later DL500s were like the FPA-4 and utilize the ALCO model 251B diesel engine as the prime mover and are rated at 1,800 horsepower (1,300 kW). All DL500s were built with C-C trucks, but B-B or paired A-1-A trucks were offered as an option. The only locale within
1785-504: The fall of 1950, an upgraded model, the FA-2, was launched. This model featured an uprated Model 244 engine, with an output of 1,600 horsepower. Additionally, the carbody was lengthened, making possible the addition of a steam generator in the A unit to allow for use in passenger service. Models equipped as such were designated the FPA-2/FPB-2. The first FA-2s were delivered in October 1950 to
1836-604: The first four locomotives with the 244 engines had been built. Two FA-1s and an FB-1 were painted in ALCO Demonstrator colors and were released for road tests for a month and a half on the Delaware and Hudson Railway . A strike at ALCO delayed production beyond the first four units and the three demonstrator units began working on the Gulf, Mobile, and Ohio Railroad in mid February 1946. The demonstrators were returned to Schenectady when
1887-501: 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
1938-471: 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
1989-701: The remainder of the order began delivery in May 1946. The GM&O order was completed in April 1947 for a total of 80 units. Before the end of this production run, ALCO upgraded the generators and traction motors in the locomotives, with the first of these models entering service in February 1947 for the New York Central . In 1950, the Montreal Locomotive Works , an affiliate of ALCO, began production of FAs as well. In
2040-509: 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
2091-455: 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
ALCO FA - Misplaced Pages Continue
2142-584: 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;
2193-591: 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
2244-461: 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
2295-420: 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
2346-570: 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
2397-496: 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
2448-503: The various FP models with the largest quantity, 38% of the total production, sold to Canadian National Railway . Some 20 units of various designations exist today in a preserved state. Several excursion railways own operating examples which are in regular service, including MLW units received from Via Rail Canada . Locomotives not sold to tourist railroads have been sold to museums and other owners. Alco built 23 A1A-A1A trucked FCA-3s for Pakistan Railways in 1951 and 1953. These were
2499-534: 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
2550-638: Was left intact, allowing the engines to be used in push-pull service with other locomotives, which usually lacked HEP. By the late 1990s and early 2000s, the railroad began retiring the ALCOs in favor of new bi-level cab cars and locomotives with HEP installed. Almost 800 FA units were built by ALCO and MLW, with just over 15% of them sold to New York Central Railroad , and another 5% each to Union Pacific Railroad , Gulf, Mobile and Ohio Railroad and Missouri Pacific Railroad . About half as many FB units were produced and sold in similar ratios. ALCO and MLW built 152 of
2601-609: 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
SECTION 50
#1732858941738#737262