The first line leading to the Richards Bay coal terminal was declared safe for the passage of trains on Thursday night, Transnet said in a statement, adding that service on the second line is expected to resume on Saturday.
The two lines have been out of service since Sunday morning after two trains collided, hitting mineral shipments already constrained by locomotive shortages as well as rampant cable theft and vandalism of infrastructure.
Coal miners Thungela Resources and Exxaro Resources said they did not expect the derailment to significantly impact their exports of the fossil fuel.
The miners have struggled for years with Transnet's limited capacity to haul commodities to ports due to equipment shortages and maintenance backlogs after decades of under-investment.
Some companies, including Thungela and Africa's top iron ore exporter Kumba Iron Ore, have been forced to cut production to match Transnet's constrained capacity to transport commodities to port.
A few miners have been moving coal to the port by road, a more expensive and environmentally damaging option than rail, but Transnet - which also operates South Africa's ports - in November announced curbs on trucks going into the Richards Bay port, citing "unprecedented congestion" on the coastal town's roads.
(Reporting by Nelson Banya; Editing by Sherry Jacob-Phillips)
