A B-unit , in railroad terminology , is a locomotive unit (generally a diesel locomotive ) which does not have a control cab or crew compartment, and must therefore be operated in tandem with another coupled locomotive with a cab (an A-unit ). The terms booster unit and cabless are also used. The concept is largely confined to North America and post-Soviet countries. Elsewhere, locomotives without driving cabs are rare.
48-464: A B-unit is distinct from a slug unit, which only has traction motors and in certain instances may have a cab. The term primarily is applied to freight locomotives, but can be applied to passenger multiple units as well in some cases for when motor cars are put in the middle of trains. In practice however, the term is rarely used to describe multiple unit trains, and in many circumstances the non-cab cars are directly or indirectly permanently attached to
96-463: A control cab if in the lead, or simply as an unpowered car in the consist. In braking it augments the powered locomotives during both dynamic and air brake application. Road slugs may take several forms. A group of GP30 , GP35 , GP38 , GP38AC , and GP40 locomotives were converted by CSX and operated as parts of mother–slug pairs. Externally they retain the general appearance of powered diesel–electric locomotives, though they can be identified by
144-463: A control cab if in the lead, or simply as an unpowered car in the consist. In braking it augments the powered locomotives during both dynamic and air brake application. Road slugs may take several forms. A group of GP30 , GP35 , GP38 , GP38AC , and GP40 locomotives were converted by CSX and operated as parts of mother–slug pairs. Externally they retain the general appearance of powered diesel–electric locomotives, though they can be identified by
192-464: A diesel–electric locomotive prime mover is capable of producing more power than its traction motors can use effectively. Extra power would cause the wheels to slip and possibly overheat the traction motors. A slug increases the number of traction motors and drive wheels available to the locomotive, increasing both the pulling and braking forces. In addition, the load on each traction motor is reduced, helping prevent overheating from excess current. Lacking
240-413: A slug is a version of a diesel–electric locomotive which lacks a prime mover and often a cab. It derives the electrical power needed to operate its traction motors and motor controls from a fully-powered mother locomotive. At low speeds the drawing (or braking ) force a diesel–electric locomotive can produce is often limited by its traction motors or the grip of its drive wheels on the track, not
288-406: A B-unit is converted from an already existing A-unit. The cab is either removed or has its windows blanked out (such as on CSX GE BQ23-7 units), and all non-essential equipment is removed. The degree to which this equipment is removed depends on the railroad, but may (and usually does) include the removal of the speedometer, event recorder, horn, headlights, toilet, and cab heaters. This conversion
336-456: A cab car. Some B-units cannot be moved without a controlling unit attached, but most have some simple controls inside, and often a side window at that control station. For example, B-unit versions of the EMD FT with conventional couplers had a fifth porthole-style window added on the right side only for the control station. Other models used existing windows. These controls enable a hostler to move
384-443: A full locomotive. A slug is distinct from a B unit , which has both a prime mover and traction motors but no cab. A slug may have an operator's cab to allow engineers to operate a train with the slug in the lead, or the cab and much of the body can be omitted to reduce cost and size, the latter allowing better visibility for an operator in the mother. A slug is used to increase adhesive weight , allowing full power to be applied at
432-451: A lower speed, thus allowing a higher maximum tractive effort. They are often used in low-speed operations such as switching operations in yards . At low speeds, a diesel–electric locomotive prime mover is capable of producing more power than its traction motors can use effectively. Extra power would cause the wheels to slip and possibly overheat the traction motors. A slug increases the number of traction motors and drive wheels available to
480-426: A prime mover, a slug typically carries ballast to improve traction, often in the form of large blocks of concrete . Slugs can be built new or converted from existing locomotives. Conversion has enjoyed popularity as a way to reuse otherwise obsolete locomotives, especially those with worn-out diesel prime movers but working traction motors. There are several types of slug, distinguished by intended use. This division
528-399: A set, train crews will often go to great lengths to arrange for the slug to be the leading unit, providing them with a more pleasant experience without the added noise and vibration from a diesel engine. Motors for added tractive effort, or MATEs, appear similar to slugs, but their design is different. Instead of siphoning off power as a slug does, the axles in a MATE are fully connected into
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#1733085277463576-399: A set, train crews will often go to great lengths to arrange for the slug to be the leading unit, providing them with a more pleasant experience without the added noise and vibration from a diesel engine. Motors for added tractive effort, or MATEs, appear similar to slugs, but their design is different. Instead of siphoning off power as a slug does, the axles in a MATE are fully connected into
624-425: A train with the slug in the lead, or the cab and much of the body can be omitted to reduce cost and size, the latter allowing better visibility for an operator in the mother. A slug is used to increase adhesive weight , allowing full power to be applied at a lower speed, thus allowing a higher maximum tractive effort. They are often used in low-speed operations such as switching operations in yards . At low speeds,
672-421: Is designed to serve as part of a regular locomotive consist for road haulage. It usually retains dynamic braking , a feature useless at the low speeds encountered in switching service, and it may be equipped to serve as a fuel tender for an attached mother locomotive. In operation, it is used to provide extra traction at low speeds. As speed increases it is disconnected from the power circuit and can function as
720-421: Is designed to serve as part of a regular locomotive consist for road haulage. It usually retains dynamic braking , a feature useless at the low speeds encountered in switching service, and it may be equipped to serve as a fuel tender for an attached mother locomotive. In operation, it is used to provide extra traction at low speeds. As speed increases it is disconnected from the power circuit and can function as
768-461: Is different. The number initially indicated the number of motorized dump cars or slugs , and the letter A or T indicated the presence of a diesel generator B-unit, but subsequently the numbers and letters lost their original meaning. Diesel locomotives: B–units of these locomotives have reduced set of driving controls, intended for service movement of the locomotive. Electric locomotives: Industrial electro-diesel locomotives: NMBS/SNCB ,
816-428: Is not absolute, and characteristics of one type may appear in another. A yard slug is designed for switching, and therefore is built to favor visibility in low-speed operation. It has a low body and no cab, allowing the engineer or driver in the powered unit to see past it. Mother–slug sets are used in heavy switching, hump yard switching, and transfer runs between yards. Some are radio-controlled without an engineer in
864-428: Is not absolute, and characteristics of one type may appear in another. A yard slug is designed for switching, and therefore is built to favor visibility in low-speed operation. It has a low body and no cab, allowing the engineer or driver in the powered unit to see past it. Mother–slug sets are used in heavy switching, hump yard switching, and transfer runs between yards. Some are radio-controlled without an engineer in
912-636: Is the equivalent of two SD40-2s . Slugs are known by other names as well. Some are: The CCRCLs (control car remote control locomotives) used by Union Pacific are sometimes called slugs. This designation is incorrect as the CCRCLs do not have traction motors. A snail, often confused with a slug, is a cabless locomotive with a prime mover. However, instead of getting electricity from a separate unit, snails have no traction motors and therefore are incapable of operating under their own power. Like slugs, snails are rebuilt from damaged or worn out locomotives and retain
960-587: Is the equivalent of two SD40-2s . Slugs are known by other names as well. Some are: The CCRCLs (control car remote control locomotives) used by Union Pacific are sometimes called slugs. This designation is incorrect as the CCRCLs do not have traction motors. A snail, often confused with a slug, is a cabless locomotive with a prime mover. However, instead of getting electricity from a separate unit, snails have no traction motors and therefore are incapable of operating under their own power. Like slugs, snails are rebuilt from damaged or worn out locomotives and retain
1008-472: Is the prime example: they were delivered new with special electrical cabinets to handle the two-to-four extra motors in a MATE. With a double-ended MATE, two U36Bs were equivalent to two U36Cs in every way. Some railroads emulated this concept by using two GP40s , then swapping in six-axle Dash 2 electrical cabinets, and then connecting the GP40s to a double-ended slug rebuilt from an old locomotive. The result
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#17330852774631056-424: Is the prime example: they were delivered new with special electrical cabinets to handle the two-to-four extra motors in a MATE. With a double-ended MATE, two U36Bs were equivalent to two U36Cs in every way. Some railroads emulated this concept by using two GP40s , then swapping in six-axle Dash 2 electrical cabinets, and then connecting the GP40s to a double-ended slug rebuilt from an old locomotive. The result
1104-484: The Illinois Central Gulf 's GP11 rebuild program, some of the engines used were ex-UP GP9Bs, and in their SD20 program, some ex-UP SD24Bs were also used. BNSF converted a former ATSF GP60B #370 into a cab unit and was renumbered to #170 in 2010. This unit was later renumbered as BNSF 200 in 2014. In rare instances, a B-unit will run at the front of a train. That is usually avoided because it limits visibility from
1152-602: The B-unit locomotive by itself in a yard or shops. B-units without controls are generally semi-permanently coupled to controlling units. Sometimes, there is a terminology distinction between the types: a 'booster' is a B-unit with hostler controls, and a 'slave' is a B-unit without hostler controls. The reasons railroads ordered B-units included the fact that a B-unit was slightly cheaper. With no driving cab, B-units lack windshields, crew seats, radios, heating, and air conditioning. There would also be no toilets, which were usually found in
1200-454: The B–unit, so getting from one locomotive to the other was no longer necessary. After extensive testing proved that the adaptions were unsuccessful, it was decided that no other units would be converted. However, 8275 was never converted back and served as Belgium's only B–unit, mostly in the port of Antwerp, until 2001, when it was scrapped after a collision with a truck. 8275 and the locomotive it
1248-447: The US, B-units of mainline diesel locomotives usually had their own model designation and received their individual numbers as independent locomotive units, not tied to any A-units. The first B-units usually used next or previous model number to model number of a corresponding A-unit (for example, ALCO DL-202 and DL-203 for A- and B-units respectively), later the model name was usually indicated by
1296-576: The USSR and later Russia, Ukraine, Kazakhstan and other post-Soviet countries, unlike the US, B-units don't have their own numbers and model designations, because they operate in a semi-fixed formations with two A-units and so considered as parts of a single multi-unit locomotive with A-B-A or A-B-B-A configuration respectively. Most of these locomotives work on BAM rail line, located on Russian Far East . Many other Russian locomotives function as semi-permanently coupled three or four unit sets. A prefix number with
1344-469: The absence of radiators and most of the access doors on the sides. They retain functional cabs and so can function as leads in strings of units. The TEBU units created on the Southern Pacific Railroad from General Electric U25Bs , on the other hand, were cabless; this potential operational deficiency was compensated for by placing them as the center units of sets of three. When at one end of
1392-402: The absence of radiators and most of the access doors on the sides. They retain functional cabs and so can function as leads in strings of units. The TEBU units created on the Southern Pacific Railroad from General Electric U25Bs , on the other hand, were cabless; this potential operational deficiency was compensated for by placing them as the center units of sets of three. When at one end of
1440-400: The cab. A hump slug is designed for even slower operation than a yard slug. They are often six-axle slugs and are often paired with lower-powered six-axle locomotives. They are designed for the specialized purpose of pushing a long cut of cars over a hump at 2 to 3 miles per hour (3 to 5 km/h), while yard slugs would normally operate at up to 15 miles per hour (24 km/h). A road slug
1488-400: The cab. A hump slug is designed for even slower operation than a yard slug. They are often six-axle slugs and are often paired with lower-powered six-axle locomotives. They are designed for the specialized purpose of pushing a long cut of cars over a hump at 2 to 3 miles per hour (3 to 5 km/h), while yard slugs would normally operate at up to 15 miles per hour (24 km/h). A road slug
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1536-429: The capability of its diesel engine(s). A slug adds more traction motors and drive wheels to both use more of the power the mother's engine can produce that cannot otherwise be used at low speeds and provide better braking, without the expense of a full locomotive. A slug is distinct from a B unit , which has both a prime mover and traction motors but no cab. A slug may have an operator's cab to allow engineers to operate
1584-412: The drawing (or braking ) force a diesel–electric locomotive can produce is often limited by its traction motors or the grip of its drive wheels on the track, not the capability of its diesel engine(s). A slug adds more traction motors and drive wheels to both use more of the power the mother's engine can produce that cannot otherwise be used at low speeds and provide better braking, without the expense of
1632-412: The frame and bogies from the original unit. Snails are used for powering engineless units and have no cab or means to control themselves manually, except from a separate unit. SP rebuilt 9 F7Bs into snails for their rotary snowplows . Some of these are still in use today with Union Pacific , along with their snowplow parent units, clearing snow on Donner Pass . Slug (railroad) In railroading,
1680-469: The intermediate units having cabs. A further advantage was that as B-units had no controls, unions were unable to insist that each unit be staffed. Finally, B-units gave a smoother, streamlined appearance to the train for passenger service. B-units were commonly built in the cab unit days in the 1930s, 1940s, 1950s, and 1960s. When hood unit road switchers became the common kind of diesel locomotive, some B-units were built, but many railroads soon came to
1728-558: The letter B at the end or in the middle of a model. The only exception is the DD35, which was initially created as B-unit before a similar A-unit with a cabin, called DD35A, appeared. At the same time, shunting cow–calf diesel locomotives with semi-permanently coupled A- and B-unit were considered a single locomotive, so a common designation for both units were used. The New York City Revenue cars 66 and 67 were R8A units which were B-units also. Diesel locomotives: Gas turbine locomotives: In
1776-537: The locomotive cab, but locomotive orientation and operational requirements may dictate that the B-unit runs first. A prominent example is the Haysi Railroad , which owned an F7B that was given radio controls and a makeshift cab. These are all known B-unit models, with discrepancies settled by the later (Marre) reference. At least one of each model was manufactured. All units below contain one or more engines and traction motors, so slugs and snails are not listed. In
1824-604: The locomotive, increasing both the pulling and braking forces. In addition, the load on each traction motor is reduced, helping prevent overheating from excess current. Lacking a prime mover, a slug typically carries ballast to improve traction, often in the form of large blocks of concrete . Slugs can be built new or converted from existing locomotives. Conversion has enjoyed popularity as a way to reuse otherwise obsolete locomotives, especially those with worn-out diesel prime movers but working traction motors. There are several types of slug, distinguished by intended use. This division
1872-403: The middle. The only exception are electric locomotives 2ES10, B-units of which received separate numbering and the «2ЭС10С» (2ES10S) type designation. In the factory documentation, the three-unit version of these locomotives often called as 3ES10, however, this designation is not used in practice. At the same time, the designation system of industrial quarry electric and electro-diesel locomotives
1920-432: The national railway company of Belgium used to operate one locomotive which could be considered a B–unit. Originally a regular Type 82 shunting locomotive, locomotive 8275 had the top half of its control cab removed. Type 82 locomotives were mostly used in pairs for shunting heavy freight trains. Because of visibility issues, the engineer would have to get from one locomotive to the other with every direction change. In 1975,
1968-673: The opinion that the lower cost of a B-unit did not offset the lack of operational flexibility. Few B-units have been built in the last 40 years. Railroads that kept ordering B-units longer than most were largely Western roads, including the Southern Pacific , Union Pacific , Burlington Northern and the Santa Fe . Santa Fe ordered the GP60B model in 1991, which were the final B-units built for road service in North America as of 2005. In some cases,
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2016-414: The railway company, seeking a solution for this problem, decided to adapt part of their Type 82 fleet. For testing purposes, 8275 had most of its cab removed, including the windows, the doors and the roof. The basic controls were left in place, covered by a removable metal plate, so it would be possible to control the locomotive on its own in case of emergency. With the cab removed, the engineer could see over
2064-408: The short hood of an A-unit. Additionally, at first, railroads bought multiple-unit diesel locomotives as one-for-one replacements for steam locomotives; as a result, railroads could not take advantage of the flexibility afforded by interchangeable units, which could be assembled into any required power output. When a three- or four-unit locomotive was considered an indivisible unit, there was no point in
2112-481: The total number of units is indicated in the model name before the main designation: «2» was used for two-unit A-A locomotives, «3» — for three-unit A-B-A locomotives and «4» — for four-unit A-B-B-A locomotives. Each unit has an additional letter after a number: letters «А» and «Б» («A» and «B») are given to two A-units, and letters «В» and «Г» («V» and «G», third and fourth letters in Russian alphabet) are given to B-units in
2160-466: The transition series in the locomotive it is connected to. A double-ended MATE (a MATE with connections on both ends) turns two four-axle locomotives into the equivalent of two fully fledged six-axle locomotives. A single-ended MATE turns a four-axle locomotive into the equivalent of an eight-axle locomotive. MATEs do not cut out at speed, as the motors are fully included in the series–parallel transition stages. Seaboard Coast Line Railroad 's GE U36B fleet
2208-466: The transition series in the locomotive it is connected to. A double-ended MATE (a MATE with connections on both ends) turns two four-axle locomotives into the equivalent of two fully fledged six-axle locomotives. A single-ended MATE turns a four-axle locomotive into the equivalent of an eight-axle locomotive. MATEs do not cut out at speed, as the motors are fully included in the series–parallel transition stages. Seaboard Coast Line Railroad 's GE U36B fleet
2256-428: Was connected to were known as 'Koe en Kalf' (cow and calf) among railway staff. Electric locomotives : Electro-diesel trainsets : Slug (railroad) In railroading, a slug is a version of a diesel–electric locomotive which lacks a prime mover and often a cab. It derives the electrical power needed to operate its traction motors and motor controls from a fully-powered mother locomotive. At low speeds
2304-642: Was sometimes performed when the A-unit had been in a collision and rebuilding the cab was not cost-effective. In some rare instances, B-units were converted to incorporate a cab, such as on the Chicago & North Western Railway in the 1970s with some EMD E8 B-units bought from the Union Pacific . The homebuilt cabs were referred to as "Crandall Cabs". Also, the Santa Fe rebuilt four of its five GP7Bs to GP9us with cabs. In
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