A weak track formation contributed to the derailment of six train wagons and damage to 15 km of track, according to a new ATSB report.
The derailment of the freight train 7SP5 occurred between Caragabal and Wirrinya, NSW on 23 October 2011.
At the time of the derailment, the train was travelling from Stockinbingal towards Parkes and was 14 hours into its journey from Sydney to Perth. The lead bogie (the undercarriage with wheels) of the 42nd wagon of the train derailed three kilometres north of Caragabal. The wheels of the bogie were dragged, off the rails, for about 15 km until they reached a turnout where six wagons separated from the train and overturned.
A dip in the track, combined with an adverse twist, caused the bogie to derail.
The ATSB found that a dip in the track, combined with an adverse twist, had caused the bogie to derail. Based on available evidence, it is likely that the track dip developed under train 7SP5 and was caused by an undetected weakness in the track formation. (The formation is the foundation of the track structure.) Track inspections had been conducted, but it is unlikely that the inspections would have identified any warning signs of formation weakness before the derailment.
Maintenance history indicated that track geometry defects had been identified and repaired around the site of the derailment, but they were generally not significant when compared to the defect that caused the derailment and defects identified and rectified in other locations along this track. Since this serious incident, the Australian Rail Track Corporation (ARTC) has implemented its Engineering Code of Practice for its rail network in NSW as part of an ongoing program of procedure standardisation across the ARTC rail network. The ATSB has urged managers and maintainers of track infrastructure to strengthen their predictive track maintenance systems by considering greater examination of historical maintenance and defect data.
Read the report: Derailment of train 7SP5, between Caragabal and Wirrinya, New South Wales, on 23 October 2011