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Drag freight
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.
== Power ==
In the mid-20th century, large locomotives such as 2-10-2s 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 inverters were made available, locomotives such as EMD SD70MAC and the GE AC4400CW replaced the older EMD SD40 on a three-for-two basis.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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