Drag freight
Encyclopedia
A drag freight is a slow, high-tonnage railroad
train, often carrying commodities such as coal
or ore
. Compared to Fast freight
trains, drag freight trains have a very low power-to-weight ratio, making them somewhat unpredictable on steep grades or hilly routes. This causes many dispatchers to be extremely conservative with how they handle drag freights, especially when they share lines with higher priority fast freights and passenger trains.
s were typically used for drag freight operations.
After the railroads dieselized, heavy duty diesel locomotives (typically six-axle units, to improve adhesion
) were used for the drag freights. Multiple unit
operations allowed one person to control multiple locomotives. As many as 4-11 locomotives may be used for a heavy haul drag freight. Attempts were made to develop ultra large locomotives for this purpose, for example the Union Pacific DDA40X and gas-turbine locomotives.
When AC traction motors coupled with thyristor
inverter
s were made available, locomotives such as EMD SD70MAC and the GE AC4400CW
replaced the older EMD SD40
on a three-for-two basis.
.
The trains were loose-coupled
, had no continuous brakes
, and were speed-limited to 25 mi/h. The lack of brake power was a potential hazard and, when approaching a downhill gradient, it was necessary to stop the train and "pin down" the handbrakes on some of the wagons before proceeding.
Today, Class 60
and Class 66
locomotives owned by the English, Welsh and Scottish Railway and Freightliner Heavy Haul are used for drag freights. Also, Class 59
locomotives owned by National Power, Foster Yeoman, and other large bulk shippers were used on the heavy freights in the 1990s. Because of coupling limits, only single units were used.
Rail transport
Rail transport is a means of conveyance of passengers and goods by way of wheeled vehicles running on rail tracks. In contrast to road transport, where vehicles merely run on a prepared surface, rail vehicles are also directionally guided by the tracks they run on...
train, often carrying commodities such as coal
Coal
Coal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure...
or ore
Ore
An ore is a type of rock that contains minerals with important elements including metals. The ores are extracted through mining; these are then refined to extract the valuable element....
. Compared to Fast freight
Fast Freight
Fast Freight may refer to:* Fast Freight , a 1929 Our Gang short* The Fast Freight, a 1921 film starring Fatty Arbuckle...
trains, drag freight trains have a very low power-to-weight ratio, making them somewhat unpredictable on steep grades or hilly routes. This causes many dispatchers to be extremely conservative with how they handle drag freights, especially when they share lines with higher priority fast freights and passenger trains.
Power
In the mid-20th century, large locomotives such as 2-10-22-10-2
Under the Whyte notation for the classification of steam locomotives, 2-10-2 represents the wheel arrangement of two leading wheels on one axle, usually in a leading truck, ten powered and coupled driving wheels on five axles, and two trailing wheels on one axle, usually in a trailing truck...
s were typically used for drag freight operations.
After the railroads dieselized, heavy duty diesel locomotives (typically six-axle units, to improve adhesion
Adhesion
Adhesion is any attraction process between dissimilar molecular species that can potentially bring them in close contact. By contrast, cohesion takes place between similar molecules....
) were used for the drag freights. Multiple unit
Multiple unit
The term multiple unit or MU is used to describe a self-propelled carriages capable of coupling with other units of the same or similar type and still being controlled from one driving cab. The term is commonly used to denote passenger trainsets consisting of more than one carriage...
operations allowed one person to control multiple locomotives. As many as 4-11 locomotives may be used for a heavy haul drag freight. Attempts were made to develop ultra large locomotives for this purpose, for example the Union Pacific DDA40X and gas-turbine locomotives.
When AC traction motors coupled with thyristor
Thyristor
A thyristor is a solid-state semiconductor device with four layers of alternating N and P-type material. They act as bistable switches, conducting when their gate receives a current trigger, and continue to conduct while they are forward biased .Some sources define silicon controlled rectifiers and...
inverter
Inverter (electrical)
An inverter is an electrical device that converts direct current to alternating current ; the converted AC can be at any required voltage and frequency with the use of appropriate transformers, switching, and control circuits....
s were made available, locomotives such as EMD SD70MAC and the GE AC4400CW
GE AC4400CW
The GE AC4400CW is a diesel-electric locomotive that was built by GE Transportation Systems between 1993 and 2004. It is similar to the Dash 9-44CW, but features AC traction motors instead of DC, with a separate inverter per motor. 2,598 examples of this locomotive were produced for North American...
replaced the older EMD SD40
EMD SD40
The EMD SD40 is a 6-axle diesel locomotive built by General Motors Electro-Motive Division between January 1966 and August 1972.-Design:Like its predecessor in EMD's catalog, the SD35, the SD40 is a high-horsepower, six-motor freight locomotive....
on a three-for-two basis.
United Kingdom
In the UK, such trains were called mineral trains and the locomotives that hauled them were called mineral locomotives. An example of a mineral locomotive was the LNWR 17in Coal EngineLNWR 17in Coal Engine
The LNWR 17in Coal Engine was a class of 0-6-0 steam tender engines designed by Francis Webb for the London and North Western Railway. They were simple locomotives and in UK service they were very reliable. "17in" refers to their cylinder diameter in inches...
.
The trains were loose-coupled
Coupling (railway)
A coupling is a mechanism for connecting rolling stock in a train. The design of the coupler is standard, and is almost as important as the railway gauge, since flexibility and convenience are maximised if all rolling stock can be coupled together.The equipment that connects the couplings to the...
, had no continuous brakes
Brake (railway)
Brakes are used on the cars of railway trains to enable deceleration, control acceleration or to keep them standing when parked. While the basic principle is familiar from road vehicle usage, operational features are more complex because of the need to control multiple linked carriages and to be...
, and were speed-limited to 25 mi/h. The lack of brake power was a potential hazard and, when approaching a downhill gradient, it was necessary to stop the train and "pin down" the handbrakes on some of the wagons before proceeding.
Today, Class 60
British Rail Class 60
The British Rail Class 60 is a class of Co-Co heavy freight diesel-electric locomotives built by Brush Traction. They are nicknamed Tugs by Rail Enthusiasts.-History:...
and Class 66
British Rail Class 66
The Class 66 is a six axle diesel electric freight locomotive developed in part from the British Rail Class 59, for use on the railways of the UK. Since its introduction the class has been successful and has been sold to British and other European railway companies...
locomotives owned by the English, Welsh and Scottish Railway and Freightliner Heavy Haul are used for drag freights. Also, Class 59
British Rail Class 59
The Class 59 Co-Co diesel locomotives were built and introduced between 1985 and 1995 by Electro-Motive Division of General Motors for private British companies, initially Foster Yeoman...
locomotives owned by National Power, Foster Yeoman, and other large bulk shippers were used on the heavy freights in the 1990s. Because of coupling limits, only single units were used.