A drag freight is a long, slow, high-tonnage

railroad Rail transport (also known as train transport) is a means of transport that transfers passengers and goods on wheeled vehicles running on rails, which are incorporated in tracks. In contrast to road transport, where the vehicles run on a pre ...

train, often carrying commodities such as

coal Coal is a combustible black or brownish-black sedimentary rock, formed as stratum, rock strata called coal seams. Coal is mostly carbon with variable amounts of other Chemical element, elements, chiefly hydrogen, sulfur, oxygen, and nitrogen ...

ore Ore is natural rock or sediment that contains one or more valuable minerals, typically containing metals, that can be mined, treated and sold at a profit.Encyclopædia Britannica. "Ore". Encyclopædia Britannica Online. Retrieved 7 April ...

. 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.

Power

Before and during WWI and into the 1920s, large locomotives such as the

2-8-2 Under the Whyte notation for the classification of steam locomotives, represents the wheel arrangement of two leading wheels on one axle, usually in a leading truck, eight powered and coupled driving wheels on four axles and two trailing wheel ...

Mikado or mainly larger types like

Articulated locomotives An articulated locomotive is a steam locomotive (rarely, an electric locomotive) with one or more engine units that can move independent of the main frame. Articulation allows the operation of locomotives that would otherwise be too large to neg ...

were typically used for drag freight operations. After the railroads dieselized, heavy duty diesel locomotives (typically six-axle units, to improve

adhesion Adhesion is the tendency of dissimilar particles or surfaces to cling to one another ( cohesion refers to the tendency of similar or identical particles/surfaces to cling to one another). The forces that cause adhesion and cohesion can b ...

) were used for the drag freights.

Multiple unit A multiple-unit train or simply multiple unit (MU) is a self-propelled train composed of one or more carriages joined together, which when coupled to another multiple unit can be controlled by a single driver, with multiple-unit train con ...

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 The EMD DDA40X is a 6,600 hp (4,943 kW) D-D locomotive, built by EMD from 1969 to 1971 exclusively for the Union Pacific Railroad. It is the most powerful diesel-electric locomotive model ever built on a single frame, having two 16-6 ...

and gas-turbine locomotives. When AC traction motors and

thyristor A thyristor () is a solid-state semiconductor device with four layers of alternating P- and N-type materials used for high-power applications. It acts exclusively as a bistable switch (or a latch), conducting when the gate receives a current t ...

inverter A power inverter, inverter or invertor is a power electronic device or circuitry that changes direct current (DC) to alternating current (AC). The resulting AC frequency obtained depends on the particular device employed. Inverters do the oppo ...

s became available, locomotives such as EMD SD70MAC and the

GE AC4400CW The GE AC4400CW, sometimes referred as "AC44CW" is a diesel-electric locomotive that was built by GE Transportation Systems between 1993 and 2004. It is like the Dash 9-44CW, but features AC traction motors instead of DC, with a separate inverter ...

replaced the older

EMD SD40 The EMD SD40 is an American 6-axle diesel-electric locomotive built by General Motors Electro-Motive Division between January 1966 and August 1972. 1,268 locomotives were built between 1966 and 1972. In 1972, an improved version with new electron ...

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 Engine. The trains were loose-coupled, had no

continuous brakes A railway brake is a type of brake used on the cars of railway trains to enable deceleration, control acceleration (downhill) or to keep them immobile when parked. While the basic principle is similar to that on road vehicle usage, operational ...

, and were speed-limited to . 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

DB Cargo UK DB Cargo UK (formerly DB Schenker Rail UK and English, Welsh & Scottish Railway (EWS)), is a British rail freight company headquartered in Doncaster, England. The company was established in early 1995 as ''North & South Railways'', successful ...

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.

External links

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