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In North American railroad terminology, a cab unit is a railroad locomotive with its own cab and controls.
"Carbody unit" is a related term, which may be either a cabless booster unit controlled from a linked cab unit, or a cab unit that contains its own controls.
With both body styles, a bridge-truss design framework is used to make the body a structural element of the locomotive. The body extends the full width and length of the locomotive. The service walkways are inside the body.
Carbody units, gaining rigidity from the body trusswork, require less structural weight to achieve rigidity than do locomotives with non-structural bodies. For that reason, carbody construction was favored to increase the power-to-weight ratio for early diesel locomotives, before the power available with diesel technology was increased. Recent years have seen carbody construction revived in the quest for greater fuel efficiency with passenger locomotives.
The full-width body gives a carbody cab unit poor rear visibility compared with a hood unit. For that reason, cab or carbody units are mostly used in situations where rear visibility is not important, such as power for through freight and passenger trains. Cab and carbody units are also more aerodynamic than hood units, and pulled many of the streamliner trains.
A cab unit is a carbody unit with a driving cab (or crew compartment). Thus, a cab unit is also always an A unit (a locomotive with a cab). By contrast, a carbody unit can be either an A unit, or a B unit (a locomotive without a cab).
A cowl unit is an adaptation of the hood unit design with a full-width body. Despite some visual similarities, cowl units are actually very different from cab units. All structural support on a cowl unit is provided by the frame of the locomotive, rather than in the body as with a cab unit. This allows manufacturers to cheaply and easily create full-width locomotives from their hood unit designs by simply adding cowling. Cowl units were first introduced as a special order from the Santa Fe, which wanted a sleeker design for its passenger equipped hood units. Although the first cowl units (such as the EMD FP45 and the GE U30CG) were meant for passenger service, EMD would later offer freight-only derivatives starting with the F45.
Cab units were not generally used in Great Britain. The traditional makers continued to use heavyweight frames and cowl units instead.
The LMS twins 10000 and 10001 used the design and later locomotive types such as the British Rail Class 37, and British Rail Class 40 utilised cab units but the term "cab unit" is not used in Britain. The Class 37 and Class 40, like most British diesel and electric locomotives, has a cab at each end.
As locomotives with a cab at each end do not have a "front" and "rear" end, the British convention is to refer to "no.1 end" or "no.2 end". No.1 end is always the end of the locomotive containing the cooler group and is usually identifiable from the exterior by large cooling grilles for the radiators.
The American Locomotive Company was an American manufacturer of locomotives, diesel generators, steel, and tanks that operated from 1901 to 1969.
Montreal Locomotive Works (MLW) was a Canadian railway locomotive manufacturer which existed under several names from 1883 to 1985, producing both steam and diesel locomotives. For a number of years it was a subsidiary of the American Locomotive Company. MLW's headquarters and manufacturing facilities were in Montreal, Quebec.
A cowl unit is a body style of diesel locomotive. The terminology is a North American one, though similar locomotives exist elsewhere. A cowl unit is one with full-width enclosing bodywork, similar to the cab unit style of earlier locomotives, but unlike the cab unit style, the bodywork is merely a casing and is not load-bearing. All the strength is in the locomotive's frame, beneath the floor, rather than the bridge-truss load-bearing carbody of the earlier type.
The EMD BL2 is a model of diesel-electric locomotive built by General Motors Electro-Motive Division (EMD). A total of 58 units were built between 1947 and 1949. The BL2 was not very successful, as it was unreliable and occupied a gap between carbody and hood units, which resulted in it suffering from the drawbacks of both designs. However, lessons learned from the BL2 were incorporated into EMD's next design, the GP7.
The ALCO RS-3 is a 1,600 hp (1.2 MW), B-B diesel-electric locomotive manufactured from May 1950 to August 1956 by American Locomotive Company (ALCO) and its subsidiary Montreal Locomotive Works (MLW). A total of 1,418 were produced: 1,265 for American railroads, 98 for Canadian railroads, 48 for Brazilian railroads, and seven for Mexican railroads.
The EMD FT is a 1,350-horsepower (1,010 kW) diesel-electric locomotive that was produced between March 1939 and November 1945, by General Motors' Electro-Motive Corporation (EMC), later known as GM Electro-Motive Division (EMD). The "F" stood for Fourteen Hundred (1400) horsepower and the "T" for Twin, as it came standard in a two-unit set. The design was developed from the TA model built for the C,RI&P in 1937, and was similar in cylinder count, axle count, length, and layout. All told 555 cab-equipped ”A” units were built, along with 541 cabless booster or ”B” units, for a grand total of 1,096 units. The locomotives were all sold to customers in the United States. It was the first model in EMD's very successful F-unit series of cab unit freight diesels and was the locomotive that convinced many U.S. railroads that the diesel-electric freight locomotive was the future. Many rail historians consider the FT one of the most important locomotive models of all time.
A hood unit, in North American railroad terminology, is a body style for diesel and electric locomotives where the body is less than full-width for most of its length and walkways are on the outside. In contrast, a cab unit has a full-width carbody for the length of the locomotive and walkways inside. A hood unit has sufficient visibility to be operated in both directions from a single cab. Also, the locomotive frame is the main load-bearing member, allowing the hood to be non-structural and easily opened or even removed for maintenance.
A road switcher is a type of railroad locomotive designed to both haul railcars in mainline service and shunt them in railroad yards. Both type and term are North American in origin, although similar types have been used elsewhere.
The Consolidation Line was a series of diesel-electric railway locomotive designs produced by Fairbanks-Morse and its Canadian licensee, the Canadian Locomotive Company. Railfans have dubbed these locomotives “C-liners”, however F-M referred to the models collectively as the C-Line. A combined total of 165 units were produced by F-M and the CLC between 1950 and 1955.
The H-24-66, or Train Master, was a diesel-electric railroad locomotive produced by Fairbanks-Morse and its licensee, Canadian Locomotive Company. These six-axle hood unit road switchers were deployed in the United States and Canada during the 1950s.
Electro-Motive Diesel is a brand of diesel-electric locomotives, locomotive products and diesel engines for the rail industry. Formerly a division of General Motors, EMD is now owned by Progress Rail, a subsidiary of Caterpillar Inc. Electro-Motive Diesel traces its roots to the Electro-Motive Engineering Corporation, founded in 1922 and purchased by General Motors in 1930. After purchase by GM, the company was known as GM's Electro-Motive Division. In 2005, GM sold EMD to Greenbriar Equity Group and Berkshire Partners, and in 2010, EMD was sold to Progress Rail. Upon the 2005 sale, the company was renamed to Electro-Motive Diesel.
The EMD GP7 is a four-axle (B-B) diesel-electric locomotive built by General Motors Electro-Motive Division and General Motors Diesel between October 1949 and May 1954.
An SDP40 is a 6-axle passenger diesel-electric locomotive built by General Motors Electro-Motive Division (EMD) between June 1966 and May 1970.
The ALCO RS-2 is a 1,500–1,600 horsepower (1,100–1,200 kW) B-B diesel-electric locomotive built by the American Locomotive Company (ALCO) from 1946 to 1950. ALCO introduced the model after World War II as an improvement on the ALCO RS-1. Between 1946 and 1950, 377 examples of the RS-2 were built, primarily for American and Canadian customers.
The ALCO DL-109 was one of six models of A1A-A1A diesel locomotives built to haul passenger trains by the American Locomotive Company (ALCO) between December, 1939 and April, 1945. They were of a cab unit design, and both cab-equipped lead A units DL-103b, DL-105, DL-107, DL-109 and cabless booster B units DL-108, DL-110 models were built. The units were styled by noted industrial designer Otto Kuhler, who incorporated into his characteristic cab the trademark three-piece windshield design. A total of 74 cab units and four cabless booster units were built.
The "Beep" is an individual switcher locomotive built in 1970 by the Atchison, Topeka and Santa Fe Railway at its Cleburne, Texas, workshops. Technically a rebuild, the Beep originally entered service on the Santa Fe as a Baldwin Model VO-1000. Following its successful CF7 capital rebuilding program, the company hoped to determine if remanufacturing its aging, non-EMD end cab switchers by fitting them with new EMD prime movers was an economically viable proposition. The conversion procedure proved too costly and only the one unit was modified. In 2008-2009, this locomotive was retired and stored operational at Topeka, Kansas. In May 2009 the unit was donated to the Western America Railroad Museum in Barstow, California.
The long hood of a hood unit-style diesel locomotive is, as the name implies, the longer of the two hoods on a locomotive, particularly American-type freight locomotives.
The ALCO FA was 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, they were of a cab unit design; both cab-equipped lead FA and cabless booster FB models were built. A dual passenger-freight version, the FPA/FPB, was also offered. It was equipped with a steam generator for heating passenger cars.
The ALCO DL-202-2 and DL-203-2 diesel-electric locomotive was an experimental freight locomotive produced by ALCO of Schenectady, New York. The primary diesel builders Alco, Baldwin and EMD pushed the War Production Board (WPB) for more opportunities to build more diesels. The Transportation Equipment Division of the WPB announced a production schedule on December 10, 1943, that allowed Alco to build one 4500 horsepower experimental diesel locomotive. This experimental diesel locomotive was to be built in the fourth quarter of 1944. The two A units were built in January 1945 and the B unit at a later date in 1945. The two A units were put on test at Building No. 37 at Schenectady to work out problems with the connecting rods and turbocharger in the Alco 241 engine, developed by both McIntosh and Seymour and ALCo. The total production run included 2 cab DL202-2 A units, and a single DL203-2 B unit. The locomotives were powered by a V12 ALCO 241 diesel engine, rated at 1,500 hp (1.1 MW). The units were released for test in September 1945. The locomotive could attain a top speed of 80 mph (130 km/h) (Freight) and 125 mph (201 km/h) (Passenger). With the B-B wheel arrangement and carbody construction, equipment layout and electrical gear these experimental units were the immediate predecessors of the FA units to come in early 1946. Outwardly, the bodies strongly resembled those on the DL-109, some of which were still under construction at Schenectady in early 1945.
A B unit, in railroad terminology, is a locomotive unit which does not have a control cab or crew compartment, and must therefore be operated in tandem with another coupled locomotive with a cab. The terms booster unit and cabless are also used. The concept is largely confined to North America. Elsewhere, locomotives without driving cabs are rare.
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