A runaway grain train with some of its wagons "likely overloaded" reached speeds of 100km/h on a section of steep winding track, according to a report into the 2020 incident.
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On December 15, 2020, the Qube train, carrying 40 loaded grain wagons, was travelling from Temora to Port Kembla when it derailed on a section of the Moss Vale-Unanderra line near Wollongong.
The train reached speeds up to 100km/h on a 30km/h section of track before it derailed and separated at two points between Dombarton and Farmborough Heights.
None of the crew, who had taken control of the train at Cootamundra, were physically injured.
The final report from the Office of Transport Safety Investigations found there were 13 factors that led to the "ineffective application of train braking systems".
"It was likely that several individual wagons were over their allowable weight limit, and the train as a whole was near, but likely not over its own maximum allowable tonnage," OTSI's Acting Chief Investigator Jim Modrouvanos said.
"In addition, variability in the braking capability between wagons likely reduced the braking effort on some wagons during the steep descent."
The final report found the wagons "had been loaded inconsistently with some wagons being heavier than others".
Overall, with a train near the maximum weight, the report said there would be "less scope for error".
"With individual wagons overloaded, the dynamics of these wagons is also affected impacting the ability of the wagon to operate as designed," the report stated.
The fact that the rails were wet and contaminated with leaf litter in some places also affected the braking ability of the train.
The final report also found that Qube's operational procedure for train management between Moss Vale and Port Kembla did not account for the dynamic braking not cutting out when the emergency brakes were applied.
"This increased the risk of the train driver avoiding the use of the emergency brake during a runaway event," the report stated.
However, Qube stated it had carried out its own studies and felt the "application of emergency braking in this instance would have likely resulted in a worse outcome".
But it had updated its procedures to recognise the dynamic brake system did not cut out when the emergency brake was applied.
The report also stated that driver fatigue may have affected some the decisions made on the morning of the derailment.
The report noted the driver had a total of 12 hours sleep over the previous 48 hours, which created "a sleep debt".
"The driver was an experienced shift worker and had descended that section of track on previous occasions and at similar times of the morning," the final report stated.
"At interview, the driver indicated they were not feeling fatigued at the time of the incident.
"The physiological effects of fatigue result from hours of wakefulness and high cognitive task demands. Individuals are not always aware of the impacts or effects and the momentary lapses in concentration which may occur as a result."