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Slug (railroad)
Encyclopedia
A railroad slug is an accessory to a diesel-electric locomotive. It has trucks
with traction motor
s but is unable to move about under its own power, as it does not contain a prime mover
to produce electricity. Instead, it is connected to a locomotive, called the mother, which provides current to operate the traction motors.
operations in yards.
At low speeds, a diesel-electric locomotive prime mover is capable of producing more electric power than its traction motors can use effectively. Extra power would simply cause the wheels to slip and possibly overheat the traction motors. A slug increases the number of traction motors available to the locomotive, increasing both the pulling and braking power. In addition the load on each traction motor is reduced, which helps prevent overheating from excess current. Slugs typically carry ballast to increase their weight and improve traction. Large blocks of concrete
are frequently used for this purpose, substituting for the weight of the now-absent prime mover.
Slugs can be built new or converted from existing locomotives. Conversion has enjoyed popularity as a way to reuse otherwise obsolete locomotives.
Road slugs are intended to serve as part of a regular locomotive consist for road haulage, and as a result have certain adaptations to suit them for this service. They usually retain dynamic brakes, a feature useless at the low speeds encountered in switching service, and they may be equipped to serve as fuel tenders
for the attached "mother" locomotives.
In operation, they are used to provide extra traction at low speeds. As speed increases they are disconnected from the power circuit and function as a control cab
if they are in the lead, or simply as an unpowered car in the consist. In braking they augment the powered locomotives, both during dynamic and air brake application.
Road slugs may take several forms. A group of GP30
and GP35
locomotives were converted by CSX
and operated as half of "mother-slug" pairs. Externally they retain the general appearance of powered diesel-electric locomotives, though they can be identified by the lack of radiator
s and the removal of most of the access doors on the side of the body. They retain the cab and its controls, and therefore multiple unit control allows them to function as the lead in a string of units. The TEBU units created on the Southern Pacific Railroad
from General Electric U25B
s, on the other hand, were cabless; this potential operational deficiency was compensated for by putting them as the center unit of a set of three. BNSF Railway
has a number of road slugs that were converted from old GP7
and GP9
locomotives, retaining their cabs and high short hoods, but with their long hoods cut down.
When at one end of a set, locomotive crews will often go to great lengths to arrange for the slug to be the leading unit, as the lack of a diesel prime mover provides them with a quiet and vibration-free ride.
fleet is the prime example: they were delivered new with special electrical cabinets to handle the 2 to 4 extra motors in a MATE. With a double-ended MATE, two U36B
s were equivalent to two U36C
s in every way.
Some railroads emulated this concept by using two GP40
s, 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 is the equivalent of two SD40-2
s.
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.
Slugs should also not be confused with snails, a term sometimes used to refer to the power source of a rotary snowplow
.
Bogie
A bogie is a wheeled wagon or trolley. In mechanics terms, a bogie is a chassis or framework carrying wheels, attached to a vehicle. It can be fixed in place, as on a cargo truck, mounted on a swivel, as on a railway carriage/car or locomotive, or sprung as in the suspension of a caterpillar...
with traction motor
Traction motor
Traction motor refers to an electric motor providing the primary rotational torque of a machine, usually for conversion into linear motion ....
s but is unable to move about under its own power, as it does not contain a prime mover
Prime mover (locomotive)
In engineering, a prime mover is an engine that converts fuel to useful work. In locomotives, the prime mover is thus the source of power for its propulsion. The term is generally used when discussing any locomotive powered by an internal combustion engine...
to produce electricity. Instead, it is connected to a locomotive, called the mother, which provides current to operate the traction motors.
Basic principles
A slug is used to increase adhesive weight, allowing full horsepower to be applied at a lower speed, thus allowing a higher maximum tractive effort. They are often used in low-speed operations such as switchingSwitcher
A switcher or shunter is a small railroad locomotive intended not for moving trains over long distances but rather for assembling trains ready for a road locomotive to take over, disassembling a train that has been...
operations in yards.
Classification yard
A classification yard or marshalling yard is a railroad yard found at some freight train stations, used to separate railroad cars on to one of several tracks. First the cars are taken to a track, sometimes called a lead or a drill...
At low speeds, a diesel-electric locomotive prime mover is capable of producing more electric power than its traction motors can use effectively. Extra power would simply cause the wheels to slip and possibly overheat the traction motors. A slug increases the number of traction motors available to the locomotive, increasing both the pulling and braking power. In addition the load on each traction motor is reduced, which helps prevent overheating from excess current. Slugs typically carry ballast to increase their weight and improve traction. Large blocks of concrete
Concrete
Concrete is a composite construction material, composed of cement and other cementitious materials such as fly ash and slag cement, aggregate , water and chemical admixtures.The word concrete comes from the Latin word...
are frequently used for this purpose, substituting for the weight of the now-absent prime mover.
Slugs can be built new or converted from existing locomotives. Conversion has enjoyed popularity as a way to reuse otherwise obsolete locomotives.
Types
There are several types of slug, distinguished by intended use. Note that as with diesel locomotives in general, this division is not absolute, and characteristics of one type may appear on another.Yard slugs
A yard slug is designed for switching, and therefore is built to increase 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 operating engineer present in the cab.Hump slugs
A hump slug is designed for even slower operation than a yard slug. They are often 6 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, while yard slugs would normally operate at up to 10 to 15 mph.Road slugs
Tender locomotive
A tender or coal-car is a special rail vehicle hauled by a steam locomotive containing the locomotive's fuel and water. Steam locomotives consume large quantities of water compared to the quantity of fuel, so tenders are necessary to keep the locomotive running over long distances. A locomotive...
for the attached "mother" locomotives.
In operation, they are used to provide extra traction at low speeds. As speed increases they are disconnected from the power circuit and function as a control cab
Control car (rail)
A control car is a generic term for a non-powered railroad vehicle that can control operation of a train from the end opposite to the position of the locomotive...
if they are in the lead, or simply as an unpowered car in the consist. In braking they augment the powered locomotives, both during dynamic and air brake application.
Road slugs may take several forms. A group of GP30
EMD GP30
The EMD GP30 was a 2,250 hp four-axle B-B diesel locomotive built by General Motors Electro-Motive Division of La Grange, Illinois between July, 1961 and November, 1963...
and GP35
EMD GP35
An EMD GP35 is a 4-axle diesel locomotive built by General Motors Electro-Motive Division between July 1963 and December 1965 and by General Motors Diesel between May 1964 and January 1966. Power was provided by an EMD 567D3A 16-cylinder engine which generated .Many railroads traded in Alco and...
locomotives were converted by CSX
CSX Transportation
CSX Transportation operates a Class I railroad in the United States known as the CSX Railroad. It is the main subsidiary of the CSX Corporation. The company is headquartered in Jacksonville, Florida, and owns approximately 21,000 route miles...
and operated as half of "mother-slug" pairs. Externally they retain the general appearance of powered diesel-electric locomotives, though they can be identified by the lack of radiator
Radiator
Radiators are heat exchangers used to transfer thermal energy from one medium to another for the purpose of cooling and heating. The majority of radiators are constructed to function in automobiles, buildings, and electronics...
s and the removal of most of the access doors on the side of the body. They retain the cab and its controls, and therefore multiple unit control allows them to function as the lead in a string of units. The TEBU units created on the Southern Pacific Railroad
Southern Pacific Railroad
The Southern Pacific Transportation Company , earlier Southern Pacific Railroad and Southern Pacific Company, and usually simply called the Southern Pacific or Espee, was an American railroad....
from General Electric U25B
GE U25B
The GE U25B was General Electric's first independent entry into the United States domestic diesel-electric railroad locomotive market for heavy production road locomotives since 1936...
s, on the other hand, were cabless; this potential operational deficiency was compensated for by putting them as the center unit of a set of three. BNSF Railway
BNSF Railway
The BNSF Railway is a wholly owned subsidiary of Berkshire Hathaway Inc., and is headquartered in Fort Worth, Texas. It is one of seven North American Class I railroads and the second largest freight railroad network in North America, second only to the Union Pacific Railroad, its primary...
has a number of road slugs that were converted from old GP7
EMD GP7
The EMD GP7 is a four-axle diesel-electric locomotive built by General Motors Electro-Motive Division and General Motors Diesel between October, 1949 and May, 1954. Power was provided by an EMD 567B 16-cylinder engine which generated . The GP7 was offered both with and without control cabs, and...
and GP9
EMD GP9
An EMD GP9 is a four-axle diesel locomotive built by General Motors' Electro-Motive Division in the United States, and General Motors Diesel in Canada between January, 1954, and August, 1963. US production ended in December, 1959, while an additional thirteen units were built in Canada, including...
locomotives, retaining their cabs and high short hoods, but with their long hoods cut down.
When at one end of a set, locomotive crews will often go to great lengths to arrange for the slug to be the leading unit, as the lack of a diesel prime mover provides them with a quiet and vibration-free ride.
MATE
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 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. SCL's GE U36BGE U36B
GE U36B was a diesel locomotive produced by General Electric beginning in 1969. The U36B was GE's 3600 horsepower answer to the power race with EMD. Only 3 railroads bought this locomotive.-History:...
fleet is the prime example: they were delivered new with special electrical cabinets to handle the 2 to 4 extra motors in a MATE. With a double-ended MATE, two U36B
GE U36B
GE U36B was a diesel locomotive produced by General Electric beginning in 1969. The U36B was GE's 3600 horsepower answer to the power race with EMD. Only 3 railroads bought this locomotive.-History:...
s were equivalent to two U36C
GE U36C
The GE U36C was a 3600 hp diesel-electric locomotive model built by GE Transportation Systems.The length of the locomotive was 67'3", standard for U30C, U33C, U34CH, U36C, U36CG, C30-7 and C36-7. The U36C also had steel capped pistons....
s in every way.
Some railroads emulated this concept by using two GP40
EMD GP40
The EMD GP40 is a 4-axle diesel-electric road switcher locomotive built by General Motors Electro-Motive Division between November 1965 and December 1971...
s, then swapping in six-axle Dash 2
EMD Dash 2
On January 1, 1972, General Motors' Electro-Motive Division introduced its new Dash 2 line of diesel-electric locomotives. All designations of these new models were those of the former models with "-2" added...
electrical cabinets, and then connecting the GP40s to a double-ended slug rebuilt from an old locomotive. The result is the equivalent of two SD40-2
EMD SD40-2
The EMD SD40-2 is a C-C locomotive produced by EMD from 1972 to 1989.The SD40-2 was first introduced in January 1972 as the mid-range offering in EMD's six-axle "Dash-2" series, competing against the GE U30C and the MLW M630...
s.
Terminology
Slugs are known by other names as well. Some are:- Drone (used by the Santa FeAtchison, Topeka and Santa Fe RailwayThe Atchison, Topeka and Santa Fe Railway , often abbreviated as Santa Fe, was one of the larger railroads in the United States. The company was first chartered in February 1859...
) - MATE (Motors for Added Tractive Effort, used by GEGE Transportation SystemsGE Transportation, formerly known as GE Rail, is a division of General Electric. The organization manufactures equipment for the railroad, marine, mining, drilling and energy generation industries. It is based in Erie, Pennsylvania. Locomotives are assembled at the Erie plant, while engine...
) - RDMT (Road MATE), used by CSX TransportationCSX TransportationCSX Transportation operates a Class I railroad in the United States known as the CSX Railroad. It is the main subsidiary of the CSX Corporation. The company is headquartered in Jacksonville, Florida, and owns approximately 21,000 route miles...
- TEBU (Tractive Effort Booster Unit, used by Morrison Knudsen and SPSouthern Pacific RailroadThe Southern Pacific Transportation Company , earlier Southern Pacific Railroad and Southern Pacific Company, and usually simply called the Southern Pacific or Espee, was an American railroad....
) - TEBC (Tractive Effort Booster Cab, BNBNBN, Bn or bn may refer to:-Organizations:* Bangladesh Navy* Barisan Nasional , a political coalition in Malaysia* Barnes & Noble, an American specialty retailer specializing in bookstore/coffeeshop venues...
/BNSF cabbed slugs) - TEBCU (Tractive Effort Booster Cab Unit, BNBNBN, Bn or bn may refer to:-Organizations:* Bangladesh Navy* Barisan Nasional , a political coalition in Malaysia* Barnes & Noble, an American specialty retailer specializing in bookstore/coffeeshop venues...
/BNSF cabbed slugs) - Hump Booster, used by Canadian National
- RDMATE (used by EMD).
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.
Slugs should also not be confused with snails, a term sometimes used to refer to the power source of a rotary snowplow
Rotary snowplow
A rotary snowplow is a piece of railroad snowfighting equipment. It is characterized by the large circular set of blades on its front end that rotate as a unit to cut through the snow on the track ahead of it.-History:...
.