RAILWAYS play a vital role in the global competitiveness of South Africa's mineral exports, and two lines built in the 1970s are critical to the efficient movement of coal and iron-ore between mines and ports. Completed in 1974, the 588km Ermelo - Vryheid - Richards Bay railway links the mines of Mpumalanga, a region that accounts for more than 80% of South Africa's coal production, with Richards Bay, the country's principal departure point for export coal. Further west, the Sishen - Saldanha iron-ore line is the world's second-longest heavy-haul railway, and opened in 1976.

While these two lines account for just 7% of the Transnet Freight Rail (TFR) network, they support the bulk of the railway's export coal and iron-ore business, which accounts for 60% of TFR's overall volumes. But despite the relative modernity of the infrastructure, both lines are struggling to meet growing demand for South African minerals.

Operations on the Ermelo - Richards Bay corridor are complex. The line descends to the coast from 1700m above sea level through an area of undulating terrain with high annual rainfall. Lines to the north of Ermelo are electrified at 3kV dc, while to the south 25kV is used, necessitating a locomotive change. Trains run in formations of up to 100 wagons from the mines to Ermelo yard, where they are coupled into pairs for the remainder of the journey south. Furthermore, capacity is constrained by the single-track section through the 4km Overvaal tunnel.

Another challenge for TFR on the Richards Bay line is the growth of general freight. TFR is keen to expand its general freight business, and it has been aided in this objective by investment at Richards Bay to accommodate greater volumes of other commodities. This means general freight trains are competing for paths on the Vryheid - Richards Bay line with coal trains, but must comply with TFR's heavy-haul operating philosophy to avoid disrupting coal traffic. In the financial year ending March 31 2011, the line carried 62.2 million tonnes of coal and 11 million tonnes of general freight, against a total capacity of 74 million tonnes and 14 million tonnes respectively.

TFR sees the potential for general freight volumes to exceed 30 million tonnes on the Richards Bay corridor, while export volumes from the Mpumalanga coalfield are expected to reach 81 million tonnes by 2016. Expansion of the coal export terminal at Richards Bay means the port can now handle 91 million tonnes per year.

Against this backdrop, the railway was beginning to look a weak link in the supply chain, and TFR is responding with a programme of system reconfiguration and incremental capacity expansion, embracing new technologies and operating practices to increase efficiency.

Important developments include the introduction of electronically-controlled pneumatic brakes (ECP), which has allowed greater operating speeds, improved train handling, faster turnaround times, and increased safety margins. ECP is being rolled out across the entire fleet of 6200 'Jumbo' coal wagons, and all new wagons delivered to the line in future will be supplied with ECP.

In addition, TFR has extensively tested bogie-mounted brake rigging, which has been found to reduce wheel temperature distribution and skew wear on brake blocks, and further reduces stopping distances when used alongside ECP.

TFR is also investing Rand 1.1bn ($US 138m) in a fleet of 110 dual-system class 19E Bo-Bo electric locomotives for the coal line, most of which have now been delivered.

These 3MW locomotives can switch between electrification systems on the move and have allowed TFR to reduce yard dwell times, while offering greater energy efficiency, and increased reliability and availability. The delivery of the 19Es has also allowed TFR to redeploy some class 7E and 10E locomotives on general freight services.

These measures are already having an impact on capacity. In the first half of last year, monthly volumes averaged 4.8 million tonnes per month, but this figure rose to 6 million tonnes per month in the second half.

TFR does not see the 26-tonne axleload and 1067mm-gauge as limiting factors for growth, but it recognises substantial investment in infrastructure will be required to facilitate expansion in both coal and general freight volumes on the Richards Bay corridor beyond 2016. Options may include longer trains, elimination of infrastructure constraints such as the Overvaal tunnel, and adoption of new wagon loading and unloading technologies.

A major development that will have a significant impact on the coal line will be the construction of an alternative route for general freight through Swaziland. On January 12 a sod-turning ceremony was held to mark the formal start of work on Swazilink, a Rand 15.9bn project that will provide a new route from Mpumalanga to Richards Bay with capacity for up to 15 million tonnes of general freight per year. It will also give Swaziland a direct rail connection to Johannesburg and Pretoria.

The project involves upgrading Transnet's line from Davel to Ermelo and Lothair, where trains will run onto a new 146km alignment which will cross the border to join the existing Swaziland Railways line from Matsapha to Phuzumoya at Sidvokodvo. The 345km Sidvokodvo - Richards Bay line, and the 154km line from Phuzumoya to Maputo in Mozambique will also be upgraded.

Speaking at the ceremony in Lothair, Transnet chief executive Mr Brian Molefe said that Swazilink will allow coal capacity on the line through Vryheid to be boosted "beyond 91 million tonnes, and closer to 100 million tonnes."

Ore line

The Sishen - Saldanha iron-ore line operates in a very different environment from the Richards Bay railway, running through a semi-desert region and descending 1295m along the 861km between the mines and the coast. With loaded trains reaching up to 41,000 tonnes and 4.1km in length, it operates at the very limits of heavy-haul technology. The line is electrified at 50kV ac and is largely single track, with passing loops sited at 40km intervals. In the 2010-11 financial year it carried 46 million tonnes of iron-ore and 1 million tonnes of general freight. Last September the line set a weekly record of 1.65 million tonnes.

Transnet has already invested in the line to boost capacity to 60.7 million tonnes per year, increasing axleloads to 30 tonnes and maximum train lengths from 216 to 342 wagons.

The fleet of 5600 CR13/14 ore wagons has been upgraded to carry a 100-tonne payload, and TFR has also taken delivery of 34 5MW class 15E electric locomotives, which are being assembled in South Africa by Union Carriage and Wagon at Nigel near Johannesburg, with a further 10 units due to arrive this year. A second batch of 32 locomotives worth Rand 898m was ordered last March which will be delivered by August 2013, allowing the line to go over to all-electric operation.

The arrival of modern locomotives is generating significant operating efficiencies. Prior to the introduction of the 15Es, a typical train was formed of three sets of 114 wagons with 10 locomotives (six diesel and three electric) positioned at four points along the train. The same 342-wagon train can now be powered by just five 15Es, crewed by one driver and one assistant using radio distributed power. This technology has reduced in-train forces, improved braking and stopping distances, and generated maintenance savings.

Through a new inventory management system, TFR now holds sufficient locomotive spares to keep the fleet running for 135 days, and there is also a strategic stock of electric locomotives components. All locomotives are subject to condition-based maintenance on a fixed time schedule, and scheduled examinations take place every 45 days.

The line's telecommunications system is being upgraded to TCS-R and GSM train communication, although TFR says the modernisation of communications infrastructure could be constrained by plans to build the so-called Square Kilometre Array (SKA) radio telescope close to the line. A final decision on whether to site this vast installation in Australia or South Africa is due later this year.

A strategy of condition-based infrastructure maintenance has been adopted to keep the ore line moving. This has involved a shift to scheduled preventative maintenance and asset-based condition inspections, supported by a range of wayside monitoring technologies including:

• hot box detectors

• wheel impact monitoring system

• wheel profile monitoring system

• skew bogie detector

• Bearing Acoustic Measurement System (Bams)

• Wayside Intelligent Long-stress Management system (Wilma), and

• ultrasonic broken rail detector system.

As with rolling stock, inventory management is key to the preventative maintenance strategy, and TFR maintains stock levels based on asset condition, budget and lead times, with 10% emergency stock supplies of all components. It also has medium and long-term contracts with approved suppliers.

Transnet is now conducting a feasibility study into how the line might be adapted to accommodate 91 million tonnes per year, although it concedes balancing the power supply and ensuring even distribution of trains will be a major challenge under these conditions without substantial investment in infrastructure. Transnet says more increases in capacity will be required on the ore line to accommodate further development of the mineral-rich Northern Cape, so that the export channel remains globally competitive, and to provide emerging and smaller mining companies in the region with access to international markets. It is also crucial to support the growth of other traffic on the line, including bulk manganese and intermodal freight, and accommodate these flows without compromising the integrity of heavy-haul operations.