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QUEENSLAND RAIL

Problem Overview

 - Constraints

 - Cycle Time

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Figure 1: Map of Queensland Coal Rail Systems

Problem Overview

QR’s heavy haul coal business operates on 5 rail corridors in Queensland.  These corridors are known as Newlands, Goonyella, Blackwater, Moura and West Moreton.  (Refer Figure 1).

Rollingstock capital is a major cost to the coal business, hence these assets need to be utilised efficiently.  QR’s coal rollingstock fleet consists of diesel and electric locomotives and bottom-dump wagons.  Diesel and electric locomotives are available in different models that vary in hauling capacity and there are 4 wagon types ranging from 73 to 104 tonne nominal capacity. 

Constraints

Certain corridor constraints restrict the rollingstock configurations that may be utilised on each corridor.  Some of these constraints are: 

• Loop length (restricts the length of the train)
• Grade or steepness (restricts the tonnage that can be hauled, i.e. the number of wagons that can be hauled by the locomotives)
• Track type and condition (restricts axle load, i.e. the wagon capacity)
• Some corridors are not electrified (Newlands, Moura, West Moreton) – hence diesel locomotives may only be utilised.

Coal Train

Loading Containers

Rollingstock related constraints include: 

• Train configurations may consist of up to 6 locomotives.
• Wagons are usually ‘strung together’ into ‘sets’.  For ease of maintenance, a set consists of the one wagon type.
• One or two sets of wagons are usually hauled in a train configuration.  The number of wagon sets that may be hauled depends on the number/capacity of the locomotives and the number/capacity of the wagons.
• Some wagon types (e.g. 104 tonne capacity) must operate in pairs – hence you cannot have an odd number of wagons in a set.
• A configuration must consist of all electric locomotives or all diesel locomotives.
• Operating electric locomotives results in energy and traction access costs.  The operation of diesels has associated fuel costs.
• Each locomotive and wagon type has differing maintenance costs. 
• It is preferable that the train configurations on a corridor are the same or similar capacity.
• It is preferable that all trains have the ability to service all mines on a corridor.  This allows flexibility and maximum utilisation of assets.
• Spare rollingstock needs to be allocated to each corridor.

QR’s engineers have determined optimal train configurations.  These consist of locomotive and wagon combinations that allow the best utilisation of the available locomotive power.  Alternative configurations for particular corridors have also been devised to allow for loop length and grade restrictions – however these configurations do not usually make optimal use of the locomotive hauling capacity.  

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Montage of Rolling Stock Products

Cycle Time

The freight cost of hauling a tonne of coal from a mine on a corridor varies for each rollingstock configuration.  One of the main factors that influences cost is cycle time.  This is the time that a train takes to travel to/from the mine and includes loading and unloading time.  Factors that influence cycle time include: 

• Higher tonnage configurations will take longer to load and unload.
• Electric trains run faster than diesel trains.
• The higher the number of trains operating on a corridor, the more time that is spent crossing trains (passing), and queuing for loading and unloading terminals.  (Note:  This also results in higher crewing costs)
• Distances for each haul on each corridor vary.

The problem involves distributing the available rollingstock in the corridors resulting in the lowest cost option.  Some rollingstock configuration options may necessitate expenditure to eliminate constraints on the corridors (e.g. increase loop length or reduce grades).  These options may be considered if the freight cost reductions achieved over time outweigh the implementation costs.

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